John Gill Commentary Exodus 6:29

"that Jehovah spake unto Moses, saying, I am Jehovah: speak thou unto Pharaoh king of Egypt all that I speak unto thee." — Exodus 6:29 (ASV)

And the Lord spoke to Moses, saying, I am the Lord
See (Exodus 6:2Exodus 6:6Exodus 6:8) : speak you to Pharaoh king of Egypt all that I say to you ;
that he let Israel go; and that in case of refusal, that he would punish him and his people with this and the other plague, one after another, and at last slay him and their firstborn.