The Catechism in Questions & Answers

233. How can we recognise what is sinful?

We learn what is sinful—in other words, what is contrary to the will of God— from Holy Scripture. This includes:

  • violations of the Ten Commandments (cf. Exodus 20: 20),
  • breaking vows given to God (cf. Deuteronomy 23: 22),
  • refusing to believe in Christ (cf. John 16: 9),
  • stinginess, envy, and the like.

This is also made clear to us in the sermon inspired by the Holy Spirit.