6 For not only in outward form did those wicked men dissemble, putting on as the Lord says sheep's clothing, and appearing like whited sepulchres; but they took those divine words in their mouth, while they inwardly cherished evil intentions. And the first to put on this appearance was the serpent, the inventor of wickedness from the beginning— the devil—who, in disguise, conversed with Eve, and immediately deceived her. But after him and with him are all inventors of unlawful heresies, who indeed refer to the Scriptures, but do not hold such opinions as the saints have handed down, and receiving them as the traditions of men, err, because they do not rightly know them nor their power.
Therefore Paul justly praises the Corinthians, because their opinions were in accordance with his traditions. And the Lord most righteously reproved the Jews, saying, 'Wherefore do you also transgress the commandments of God on account of your traditions.' For they changed the commandments they received from God after their own understanding, preferring to observe the traditions of men. And about these, a little after, the blessed Paul again gave directions to the Galatians who were in danger thereof, writing to them, 'If any man preach to you anything else than that you have received, let him be accursed.'
Source: Letters (New Advent)