God does not have to save anyone who has fallen in Sin, though He justly does save some.

"Lastly, if it was not incompatible with God's infinite goodness to pass by the whole body of fallen angels and leave them under the guilt of their apostasy, much less can it clash with that attribute to pass by some of fallen mankind and resolve to leave them in their sins and punish them for them. Nor is it inconsistent with Divine justice to withhold saving grace from some, seeing the grace of God is not what He owes to any. It is a free gift to those that have it, and it is not due to those that are without it; consequently there can be no injustice in not giving what God is not bound to bestow. There is no end of caviling at the Divine dispensations if men are disposed to do it. We might, with equality of reason, when our hand is in, presume to charge the Deity with partiality for not making all His creatures angels because it was in His power to do so, as charge Him with injustice for not electing all mankind. Besides, how can it possibly be subversive of His justice to condemn, and resolve to condemn, the non-elect for their sins when those very sins were not atoned for by Christ as the sins of the elect were? His justice in this case is so far from hindering the condemnation of the reprobate that it renders it necessary and indispensable. Again, is the decree of sovereign preterition and of just condemnation for sin repugnant to the Divine holiness? Not in the least, so far from it, that it does not appear how the Deity could be holy if He did not hate sin and punish it. Neither is it contrary to His truth and veracity. Quite the reverse. For would not the Divine veracity fall to the ground if the finally wicked were not condemned?" - Jerome Zanchius, Absolute Predestination

The proper use of means in Predestination

'Although,' to use the words of Gregory, 'God never swerves from His decree, yet He often varies in His declarations': that is always and immoveable; these are sometimes seemingly discordant. So when He gave sentence against the Ninevites by Jonah, saying, 'Yet forty days, and Nineveh shall be overthrown,' the meaning of the words is not that God absolutely intended, at the end of that space, to destroy the city, but that, should God deal with those people according to their deserts, they would be totally extirpated from the earth, and should be so extirpated unless they repented speedily.
Likewise, when He told King Hezekiah by the prophet Isaiah, 'Set thine house in order, for thou shalt die and not live,' the meaning was that with respect to second causes, and, considering the king's bad state of health and emaciated constitution, he could not, humanly speaking, live much longer. But still the even showed that God had immutably determined that he should live fifteen years more, and in order to that had put it into his heart to pray for the blessing decreed, just as, in the case of Nineveh, lately mentioned, God had resolved not to overthrow that city then; and, in order to the accomplishment of His own purpose in a way worthy of Himself, made the ministry of Jonah the means of leading that people to repentance. All which, as it shows that God's absolute predestination does not set aside the use of means, so does it likewise prove that, however various the declarations of God may appear (to wit, when they proceed on a regard had to natural causes), His counsels and designs stand firm and immovable, and can neither admit of alteration in themselves, nor of hindrance in their execution. See this farther explained by Bucer in Rom. 9, where you will find the certainty of the Divine appointment solidly asserted and unanswerably vindicated." - Jerome Zanchius, Absolute Predestination

Secondary Causes still upheld

"The influence which the Divine foreknowledge has on the certain futurition of the things foreknown does not render the intervention of second causes needless, nor destroy the nature of the things themselves."- Jerome Zanchius, Absolute Predestination

Nothing happens but because God willed it to be so

"We assert that God did from eternity decree to make man in His own image, and also decreed to suffer him to fall from that image in which he should be created, and thereby to forfeit the happiness with which he was invested, which decree and the consequences of it were not limited to Adam only, but included and extended to all his natural posterity.
Something of this was hinted already in the preceding chapter, and we shall now proceed to the proof of it.
(1) That God did make man in His own image is evident from Scripture (Gen. 1. 27).
(2) That He decreed from eternity so to make man is as evident, since for God to do anything without having decreed it, or fixed a previous plan in His own mind,  would be a manifest imputation on His wisdom, and if He decreed that now, or at any time, which He did not always decree, He could not be unchangeable.
(3) That man actually did fall from the Divine image and his original happiness is the undoubted voice of Scripture (Gen. 3), and
(4) That he fell in consequence of the Divine decree we prove thus: God was either willing that Adam should fall, or unwilling, or indifferent about it. If God was unwilling that Adam should transgress, how came it to pass that he did? Is man stronger and is Satan wiser than He that made them? Surely no. Again, could not God, had it so pleased Him, have hindered the tempter's access to paradise? or have created man, as He did the elect angels, with a will invariably determined to good only and incapable of being biased to evil? or, at least have made the grace and strength, with which He endued Adam, actually effectual to the resisting of all solicitations to sin? None but atheists would answer these questions in the negative. Surely, if God had not willed the fall, He could, and no doubt would, have prevented it; but He did not prevent it: ergo, He willed it. And if He willed it, He certainly decreed it, for the decree of God is nothing else but the seal and ratification of His will. He does nothing but what He decreed, and He decreed nothing which He did not will, and both will and decree are absolutely eternal, though the execution of both be in time. The only way to evade the force of this reasoning is to say that 'God was indifferent and unconcerned whether man stood or fell.' But in what a shameful, unworthy light does this represent the Deity! Is it possible for us to imagine that God could be an idle, careless spectator of one of the most important events that ever came to pass? Are not 'the very hairs of our head all numbered'? or does 'a sparrow fall to the ground without our heavenly Father'? If, then, things the most trivial and worthless are subject to the appointment of His decree and the control of His providence, how much more is man, the masterpiece of this lower creation? and above all that man Adam, who when recent from his Maker's hands was the living image of God Himself, and very little inferior to the angels! and on whose perseverance was suspended the welfare not of himself only, but likewise that of the whole world. But, so far was God from being indifferent in this matter, that there is nothing whatever about which He is so, for He worketh all things, without exception, 'after the counsel of His own will' (Eph. 1. 11), consequently, if He positively wills whatever is done, He cannot be indifferent with regard to anything. On the whole, if God was not unwilling that Adam should fall, he must have been willing that he should, since between God's willing and nilling there is no medium. And is it not highly rational as well as Scriptural, nay, is it not absolutely necessary to suppose that the fall was not contrary to the will and determination of God? since, if it was, His will (which the apostle represents as being irresistible, Rom 9. 19) was apparently frustrated and His determination rendered of worse than none effect. And how dishonourable to, how inconsistent with, and how notoriously subversive of the dignity of God such a blasphemous supposition would be, and how irreconcileable with every one of His allowed attributes is very easy to observe. . . ." - Jerome Zanchius, Absolute Predestination

Justification only for the elect in Christ alone

"God, as we have before proved, wills not the salvation of every man, but He gave His Son to die for them whose salvation He willed; therefore His Son did not die for every man. All those for whom Christ died are saved, and Divine justice indispensably requires that to them the benefits of His death should be imparted; but only the elect are saved, they only partake of those benefits, consequently for them only He died and intercedes. The apostle (Rom. viii.) ask, 'who shall lay anything to the charge of God's elect? it is God that justifies,' i.e., His elect, exclusively of others; 'who is He that condemneth? It is Christ that died' for them, exclusive of others. The plain meaning of the passage is that those whom God justifies, and for whom Christ died (justification and redemption being of exactly the same extent), cannot be condemned. These privileges are expressly restrained to the elect: therefore God justifies and Christ died for them alone." - Jerome Zanchius, Absolute Predestination

Justification is by Grace alone imputed through Faith alone in Christ alone

"It is indeed true that in the sight of men a man is made good or evil by his works; but this being made good or evil only means that the man who is good or evil is pointed out and known as such, as Christ says in Matt. 7 [:20], 'Thus you will know them by their fruits.' All this remains on the surface, however, and very many have been deceived by this outward appearance and have presumed to write and teach concerning good works by which we may be justified without even mentioning faith. They go their way, always being deceived and deceiving [II Tim. 3:13], progressing, indeed, but into a worse state, blind leaders of the blind, wearying themselves with many works and still never attaining to true righteousness [Matt. 15:14]. Of such people Paul says in II Tim. 3 [5, 7], "Holding the form of religion but denying the power of it . . . who will listen to anybody and can never arrive at a knowledge of the truth.'
Whoever, therefore, does not wish to go astray with those blind men must look beyond works, and beyond laws and doctrines about works. Turning his eyes from works, he must look upon the person and ask how he is justified. For the person is justified and saved, not by works or laws, but by the Word of God, that is, by the promise of his grace, and by faith, that glory may remain God's, who saved us not by works of righteousness which we have done [Titus 3:5], but by virtue of his mercy by the word of his grace when we believe [1 Cor. 1:21].
From this it is easy to know how far good works are to be rejected or not, and by what standard all the teachings of men concerning works are to be interpreted. If works are sought after as a means to righteousness, are burdened with this perverse leviathan, and are done under the false impression that through them one is justified, they are made necessary and freedom and faith are destroyed; and this addition to them makes them no longer good but truly damnable works. They are not free, and they blaspheme the grace of God since to justify and to save by faith belongs to the grace of God alone. What the works have no power to do they nevertheless - by a godless presumption through this folly of ours - pretend to do and thus violently force themselves into the office and glory of grace. We do not, therefore, reject good works; on the contrary, we cherish and teach them as much as possible. We do not condemn them for their own sake but on account of this godless addition to them and the perverse idea that righteousness is to be sought through them; for that makes them appear good outwardly, when in truth they are not good. They deceive men and lead them to deceive one another like ravening wolves in sheep's clothing [Matt. 7:15]."
- Martin Luther, The Freedom of a Christian, Pg. 38 - 39

The Christian's justification by Faith alone apart from works

"A good or bad house does not make a good or bad builder; but a good or bad builder makes a good or bad house. And in general, the work never makes.workman like itself, but the workman makes the work like himself. So it is with the works of man. As the man is, whether believer or unbeliever, so also is his work - good if it was done in faith, wicked if it was done in unbelief. But the converse is not true, that work makes the man either a believer or an unbeliever. As works do not make a man a believer, so also they do not make him righteous. But as faith makes a man a believer and righteous, so faith does good works. Since, then, works justify no one, and a man must be righteous before he does a good work, it is very evident that it is faith alone which, because of the pure mercy of God through Christ and in his Word, worthily and sufficiently justifie and saves the person. A Christian has no need.of any work or law in order to be saved since through faith he is free from every law and does everything out of pure liberty and freely." - Martin Luther, The Freedom of a Christian, Pg. 37

Martin Luther - a benefit of Faith

"The third incomparable benefit of faith is that it unites the soul with Christ as a bride is united with her bridegroom. By this mystery, as the Apostle teaches, Christ and the soul become one flesh [Eph. 5:31-32]. And if they are one flesh and there is between them a true marriage - indeed the most perfect of all marriages, since human marriages are but poor examples of this one true marriage - it follows that everything they have they hold in common, the good as well as the evil. Accordingly the believing soul can boast of and glory in whatever Christ has as though it were its own, and whatever the soul has Christ claims as his own. Let us compare these and we shall see inestimable benefits. Christ is full of grace, life, and salvation. The soul is full of sins, death, and damnation. Now let faith come between them and sins, death, and damnation will be Christ's, while grace, life, and salvation will be the soul's; for if Christ is a bridegroom, he must take upon himself the things which are his bride's and bestow upon her the things that are his. If he gives her his body and very self, how shall he not give her all that is his? And if he takes the body of the bride, how shall he not take all that is hers?"
- Martin Luther, The Freedom of a Christian

The Gospel in its wide and narrow sense

I have posted up another quote from Walther of a paragraph just above this one. If you want you can read that before this one. I wanted this separately because of emphasis to stress the distinction between the Gospel in its wide and narrow sense.

"There is a similar usage as regards the term Gospel; sometimes it is used in a wide, then again in a narrow meaning. The narrow meaning is its proper sense; in its wide meaning it is used merely by way of synecdoche, signifying anything that Jesus preached, including even His very poignant preaching of the Law, as, for instance, the Sermon on the Mount and His reproving of wicked men. Besides the term Gospel is used in contradistinction to the Old Testament, which often signifies only the teaching of the Law." - C.F.W. Walther, The Proper Distinction between Law and Gospel

Repentance in its Narrow sense and Broad sense

"The term repentance is used in a narrow sense to signify the knowledge of sin and heartfelt sorrow and contrition. In Mark 1, 15 we read: 'Repent ye and believe the Gospel.' In this statement John the Baptist evidently did not include faith in repentance, otherwise his statement would be tautological. In Acts 20, 21 Paul relates that he had been 'testifying both to the Jews and also to the Greeks, repentance toward God and faith toward our Lord Jesus Christ.'  Since faith is named separately in this text, the term repentance cannot embrace knowledge of sin, contrition, and faith. Likewise, the Lord says concerning the Jews that despite the preaching of John the Baptist they 'repented not afterward that they might believe him,' Matt. 21, 32 . . . . By repentance he refers to the effects of the law and means to say that, since they had not become alarmed over their sins, it had not been possible for them to believe. For there will not be faith in a heart that has not first been terrified." - C.F.W Walther, The Proper Distinction between Law and Gospel

The importance of the difference between Law and Gospel

It is very important to know the difference between the two principle points of Christianity or else one would become liable to the charge of legalism or licentiousness.

"By 'the law' here is meant the moral law as a covenant of works, and by 'the gospel' is meant the gospel in its strict and proper sense. To know the differemce so as to be able to distinguish aright between the law and the gospel is of every itmost importance to the faith, holiness, and comfort of every true Christian. It will be impossible otherwise for a man so to believe as to 'be filled with joy and peace in believing.' If he does not know the difference between the law ...and the gospel he will be apt, especially in affair of justification, to confound the one with the other. The consequence will be that his painful experience, bondage will be mixed with liberty of spirit, fear with hope, sorrow with joy, and death with life. If he cannot so distinguish the gospel from the law as to expect all his salvation from the grace of the gospel, and nothing of it from the works of the law; he will easily be induced to connect his own works with the righteousness of Jesus Christ in the affair of his justification. This was the great error of the Judaizing teachers in the churches of Galatia. They mingled the law with the gospel in the business of justification, and thereby they so corrupted the gospel as to alter the very natof it and make it another gospel. They taught that unless men were circumcised and kept the law of Moses, they could not be justified or saved (Acts 15:1-5). They informed the people that while the righteousness of Christ received by faith was necessary, their own works of obedience were also requisite in connection with it to entitle them to justification before God. This is a fundamental error, and such a one that if even an angel from heaven would publish it he should be accursed." -John Colquhoun, A Treatise on the Law and Gospel

"The principal DIFFERENCES between these two parts of the doctrine of the church, consist in these three things:

1. In the subject, or general character of the doctrine, peculiar to each. The law prescribes and enjoins what is to be done, and forbids what ought to be avoided: whilst the gospel announces the free remission of sin, through and for the sake of Christ.
2. In the manner of the revelation peculiar to each. The law is known from nature; the gospel is divinely revealed.
3. In the promises which they make to man. The law promises life upon the condition of perfect obedience; the gospel, on the condition of faith in Christ and commencement of new obedience. Hereafter, however, more will be said upon this subject in the proper place." - The Commentary on the Heidelberg Catechism by Zacharias Ursinus

The Christian is not under the law in its covenantal form

"The law as the law of Christ has no sanction of judicial rewards or punishments. It has no promise of eternal life or threatening of eternal death annexed to it. The form of the covenant of works, indeed, is eternally binding on all who live and die under that violated covenant, but because Christ, as last Adam, has answered all the demands of it for believers, they are delivered from the law in that form (Romans 7:4-6)." - John Colquhoun, A Treatise on the Law and the Gospel