Martin Luther on what a true Christian community is

Martin Luther on what a true Christian community is:

It is necessary, first of all, to know where and what a Christian community is so that men may not engage in purely human affairs under cover of the name of a Christian church, as has always been the custom of non-Christians. The certain mark by which a Christian community can be recognized is the preaching of the gospel in its purity. Just as one can tell by the military banner, as by a sure sign, what leader and what army have taken the field, so one may surely know by the gospel where Christ and his people are stationed. Of this we have God's sure promise in Isaiah 55 [:10, 11], 'My word that goes forth from my mouth shall not return to me empty, but as the rain comes down from heaven and waters the earth, so shall my word accomplish that which I purpose.' Hence we are certain that where the gospel is preached there must be Christians, no matter how few in number or how sinful and weak they may be. We are just as certain that where the gospel is not preached and where the doctrines of men hold sway there can be no Christians but only heathen, no matter how great their numbers or how pious and good their lives.
From this it follows unquestionably that the bishops, foundations, monastic houses, and all the rest of that crew have long since ceased to be either Christians or a Christian community, though they have flaunted this name as their exclusive possession. Anybody who knows what the gospel is can see, hear, and understand that to this very day they rely on their human teachings and have altogether rejected, and are still rejecting, the gospel. Whatever such people do and say must therefore be regarded as heathen and of this world." - Martin Luther, Right and Power of a Christian Church, Pg. 325-326