Romans 4:17 - God, who gives life to the dead and calls those things which do not exist as though they did.
Of course, it’s not remotely about the power of our words; it is about the power of God’s promises and His faithfulness to keep those promises. Our promises won’t show up because we “confessed” or “declared” certain words but because God promised he would do it.
Romans 4:21 - and being fully convinced that what He had promised He was also able to perform.