Chapter 25 — Part III: The Decalogue — The Second Commandment
Section 16. Meaning Of An Oath — Since in explaining this part of the Commandment the chief object is to teach the faithful how to render an oath reverential and holy, it is first to be observed, that to swear, whatever the form of words may be, is nothing else than to call God to witness; thus to say, God is witness, and By God, mean one and the same thing.