Conversion is a work of God alone

"It is necessary, on the other hand, to consider the remedy of Divine grace, by which the depravity of nature is corrected and healed. For since the Lord in the assistance which he affords us, bestows on us that which we need, an exhibition of the nature of his work in us will immediately discover the nature of our necessity. When the Apostle tells the Philippians, that he is 'confident that he which hath begun a good work in them will perform it until the day of Jesus Christ;' by the beginning of a good work he undoubtedly designs the commencement of conversion, which takes place in the will. Therefore God begins the good work in us by exciting in our hearts a love, desire, and ardent pursuit of righteousness, or, to speak more properly, by bending, forming, and directing our hearts toward righteousness, but he completes it, by confirming us to perseverance. That no one may cavil, that the good work is begun by the Lord, inasmuch as the will, which is weak of itself, is assisted by him, the Spirit declares in another place how far the ability of the will reaches, when left to itself. 'a new heart also,' says he, 'will I give you, and a new spirit will I put within you; and I will take away the stony heart out of your flesh, and I will give you a heart of flesh. And I will put my Spirit within you, and cause you to walk in my statutes.' Who will assert that the infirmity of the human will is only strengthened by assistance, to enable it efficaciously to aspire to the choice of that which is good, when it actually needs a total transformation and renovation?" - John Calvin, Insistutes, 2. 3. 6.