Chapter 31 — Part III: The Decalogue — The Eighth Commandment
Section 26. This Commandment Forbids Hypocrisy — Finally, the first part of this Commandment prohibits dissimulation. It is sinful not only to speak, but to act deceitfully. Actions, as well as words, are signs of what is in our mind; and hence our Lord, rebuking the Pharisees, frequently calls them hypocrites. So, far with regard to the negative, which is the first part of this Commandment.