13 The task of the catechist is to take up one or other of the truths of faith or of Christian morality and then explain it in all its parts; and since amendment of life is the chief aim of his instruction, the catechist must needs make a comparison between what God commands us to do and what is our actual conduct. After this, he will use examples appropriately taken from the Holy Scriptures, Church history, and the lives of the saints - thus moving his hearers and clearly pointing out to them how they are to regulate their own conduct. He should, in conclusion, earnestly exhort all present to dread and avoid vice and to practice virtue.
Source: Acerbo Nimis (Vatican.va)