The church of God on earth, even when it is at the best, has wicked people and hypocrites in it. In Adam’s family there is Cain, in the ark there is Ham, in Christ’s family or school there is Judas. In the church of Jerusalem, planted and governed by the chief apostles, there are false brethren. The true sheep are often without and wolves within. Therefore we may not so much as dream of a perfection of the church of God on earth so long as wicked people are mixed with true believers.
William Perkins, 16th century theologian, Commentary on Galatians