Isaiah 45:23 - Matthew Poole's English Annotations on the Holy Bible

I have sworn by myself, which is the highest and most solemn oath that is possible, Hebrews 6:13, and therefore signifies that the matter here sworn is of an extraordinary importance. The word is gone out of my mouth in righteousness; it is not a vain word rashly uttered, and afterwards never remembered nor observed, but what I sincerely speak, and will most faithfully and infallibly perform. Shall not return, to wit, unto me void, or without effect, as this phrase is more fully delivered, Isaiah 55:11. It is a metaphor from ambassadors, who sometimes return to their princes without any success in their business. Unto me every knee shall bow, every tongue shall swear; not only the Jews, but a people of all nations, shall worship me, and submit to my laws; which is signified by an outward act, the bowing of the knee, Which is a posture of reverence and subjection; and by one eminent part of God's worship, which is swearing by his name.