Roman Catechism 26.38

Chapter 26 — Part III: The Decalogue — The Third Commandment

Section 38. These words teach us, in the first place, to avoid whatever may interfere with the worship of God. Hence it is not difficult to perceive that all servile works are forbidden, not because they are improper or evil in themselves, but because they withdraw the attention from the worship of God, which is the great end of the Commandment.