John Calvin Commentary Isaiah 14:24

"Jehovah of hosts hath sworn, saying, Surely, as I have thought, so shall it come to pass; and as I have purposed, so shall it stand:" — Isaiah 14:24 (ASV)

The Lord of hosts has sworn. For fuller confirmation, an oath was necessary. There is nothing more difficult to convince us of than that wicked men will immediately be ruined when we see them flourishing, furnished with all means of defense, and seemingly placed out of danger and free from all fear. We are therefore stunned by beholding them and are dazzled by their brightness, so that we can scarcely believe God when he foretells their ruin and destruction. For this reason, he employs an oath, so that he may leave no room for doubt. From this we learn how great his forbearance towards us is, when he aids our weakness by applying this remedy, for otherwise he might have been satisfied with simply declaring it. This tends to the consolation of the godly, as we will later see (Isaiah 22:14).

If it has not been as I thought. The elliptical form of an oath which he employs must be well known, for it occurs frequently in Scripture. The Lord purposely used this guarded language, so that we might not be too free in the use of oaths, which burst from us daringly and at random. He suppresses the greater part of the oath. “If I do not do what I have decreed, let men think that I am a liar, and let them not think that I am God;” or something of this kind (which we shudder to express) is left to be supplied. Men ought, therefore, to put a bridle on themselves, so as not to break out at random into imprecations or to pronounce shocking curses against themselves; but let them learn from this to restrain their insolence.