Dietrich Bonhoeffer, arguing that Christian sanctification requires identification with the visible church-community:

A merely personal sanctification which seeks to bypass [the] openly visible separation of the church-community from the world confuses the pious desires of the religious flesh with the sanctification of the church-community, which has been accomplished in Christ’s death and is being actualized by the seal of God. It is the deceptive pride and the false spiritual desire of the old, sinful being that seeks to be holy apart from the visible community of Christians. Contempt for the body of Christ as the visible community of justified sinners is what is really hiding behind the apparent humility of this kind of inwardness. It is indeed contempt for the body of Christ, since Christ was pleased visibly to assume my flesh and to carry it to the cross. It is contempt for the community, since I seek to be holy apart from other Christians. It is contempt for sinners, since in self-bestowed holiness I withdraw from my church in its sinful form. Sanctification apart from the visible church-community is mere self-proclaimed holiness.