Roman Catechism 23.21

Chapter 23 — Part III: The Decalogue — Introduction on the Commandments in General

Section 21. In our observance of the law, however, we should not act so much for our own advantage as for the sake of God who, by means of the law, has revealed His will to man. If other creatures are obedient to God's will, how much more reasonable that man should follow it?