See now that I am, even I am he. The Hebrew is more expressive, See now that I, I am; LXX; ἴδετε ἴδετε ὅτι ἐγώ εἰμι (cf. Isaiah 41:4; Isaiah 48:12; John 8:24, John 18:5). Their own experience of the utter impotency of these idol-gods to help them or to protect themselves from the stroke of the Almighty was enough to convince them that they were no gods, and that he alone was to be feared and worshipped.
These verses should be read continuously: For I lift up my hand to heaven, and say, As I live forever, if I whet my glittering sword, and if my hand take hold on judgment; I will render vengeance to mine enemies, etc. Lifting up the hand to heaven was a gesture intended to express that the person taking an oath appealed to God as a witness of his oath, and who would perish for falsehood (cf. Genesis 14:22); and "as the Lord liveth" was a common formula in taking an oath (cf. Numbers 14:21; 1 Samuel 14:39, 1 Samuel 14:45; Jeremiah 5:2). As God could swear by none greater, he swore by himself (cf. Exodus 6:8; Numbers 14:30; Isaiah 45:23; Jeremiah 22:5; Hebrews 6:17), that if he did come forth to avenge himself of his enemies, he would not spare, but would do thoroughly what he had come forth to do.—Glittering sword; literally, lightning of sword (cf. Ezekiel 21:10 (15)).