Catechism of the Catholic Church §1454 — excerpt
The reception of this sacrament ought to be prepared for by an examination of conscience made in the light of the Word of God. the passages best suited to this can be found in the moral catechesis of the Gospels and the apostolic Letters, such as the Sermon on the Mount and the apostolic teachings.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Whole chapters cited: Matthew 5 · Matthew 6 · Matthew 7 · Romans 12 · Romans 13 · Romans 14 · Romans 15 · 1 Corinthians 12 · 1 Corinthians 13 · Galatians 5 · Ephesians 4 · Ephesians 5 · Ephesians 6