The Catechism in Questions & Answers

364. What is the meaning of the Ninth and Tenth Commandments for us today?

The Ninth and Tenth Commandments assign mankind the task of watching over the purity of their hearts. They are to fight off any temptation to sinful actions.

“As obedient children, not conforming yourselves to the former lusts, as in your ignorance; but as He who called you is holy, you also be holy in all your conduct.”
1 Peter 1: 14-15