36 Make thou your fold with the sheep: flee from the wolves: depart not from the Church. Hate those also who have ever been suspected in such matters: and unless in time thou perceive their repentance, do not rashly trust yourself among them. The truth of the Unity of God has been delivered to you: learn to distinguish the pastures of doctrine. Be an approved banker, holding fast that which is good, abstaining from every form of evil. Or if you have ever been such as they, recognise and hate your delusion. For there is a way of salvation, if you reject the vomit, if you from your heart detest it, if you depart from them, not with your lips only, but with your soul also: if you worship the Father of Christ, the God of the Law and the Prophets, if you acknowledge the Good and the Just to be one and the same God. And may He preserve you all, guarding you from falling or stumbling, established in the Faith, in Christ Jesus our Lord, to Whom be glory for ever and ever. Amen.
Source: Catechetical Lectures (New Advent)