On the Church Militant (or Visible)

The state of the church has always been such that some were called the people and saints of God who were not so, while others, who were among them as a remnant, were the people and saints of God, but were not so called. However, Christ has preserved His church, though not so as to be called the church.

I do not say this because I deny that those whom you cite are the saints and church of God, but because it cannot be proved that they really are saints, should anyone deny it. I call them saints, and so regard them; I call them the church, and so judge them—but by the rule of charity, not by the rule of faith. By which I mean that charity, which always thinks the best of everyone, and is not suspicious, but believes and assumes all good of its neighbour, calls every baptized person a saint. There is no danger involved if she is wrong; it is the way of charity to be deceived, for she is open to all the uses and abuses of every man, as being handmaid of all, good and bad, believing and unbelieving, true and false. Faith, however, calls none a saint but him who is proclaimed such by divine sentence, for the way of faith is not to be deceived.

—Martin Luther, The Bondage of the Will, p121-122.