John Gill Commentary Isaiah 45:23

"By myself have I sworn, the word is gone forth from my mouth [in] righteousness, and shall not return, that unto me every knee shall bow, every tongue shall swear." — Isaiah 45:23 (ASV)

I have sworn by myself Christ being the true God, he could swear by no greater, (Hebrews 6:13), this shows that what follows, and is here sworn to, is of great importance, and strictly true, and would certainly be accomplished:

the word is gone out of my mouth in righteousness; both what goes before, that such that look to him shall be saved; and also what follows, concerning the subjection of every creature to him; this was what he had resolved in his mind, and declared in his word, by promise and prophecy, should be; and as it was agreeable to truth and justice, it should certainly, and in faithfulness, be performed, and shall not return void and without effect, but be exactly and punctually accomplished:

that to me every knee shall bow, every tongue shall swear; that is, everyone, or at least the generality of mankind, shall be subject to Christ, embrace his Gospel, submit to his ordinances, profess his name, and serve and worship him; this will be when the fulness of the Gentiles is brought in, and the Jews are converted: the apostle quotes this passage, and applies it to the judgment day, when all, whether they will or not, shall confess that Christ is God, which he so often asserts in this context; see (Romans 14:10Romans 14:11) (Philippians 2:10Philippians 2:11).