... Thus whenever Paul writes to Christians, he calls them saints, sons and heirs of God, etc. Therefore saints are all those who believe in Christ, whether men or women, whether slaves or free. And they are saints, on the basis, not of their own works but of the works of God, which they accept by faith, such as the Word, the sacraments, the suffering, death, resurrection, and victory of Christ, the sending of the Holy Spirit, etc. In other words, they are saints, not by active holiness but by passive holiness.

Such genuine saints include ministers of the Word, political magistrates, parents, children, masters, servants, etc., if they, first of all, declare that Christ is their wisdom, righteousness, sanctification, and redemption (1 Cor. 1:30), and if, in the second place, they all do their duty in their callings on the basis of the command of the Word of God, abstaining from the desires and vices of the flesh for the sake of Christ. They are not all of equal firmness of character, and many weaknesses and offenses are discernible in every one of them; it is also true that many of them fall into sin. But this does not hinder their holiness at all, so long as they sin out of weakness, not out of deliberate wickedness. For, as I have already said several times, the godly are conscious of the desires of the flesh; but they resist them and do not gratify them. When they fall into sin unexpectedly, they obtain forgiveness, if by faith they return to Christ, who does not want us to chase away the lost sheep but to look for it. On no account, therefore, am I to jump to the conclusion that those who are weak in faith or morals are unholy, when I see that they love and revere the Word, receive the Lord's Supper, etc.; for God has received them and regards them as righteous through the forgiveness of sins. It is before Him that they stand or fall (Rom. 14:4).

Luther's 1535 Galatians Commentary

LW, AE vol. 27, p. 82