Charles Ellicott Commentary Exodus 4:22

"And thou shalt say unto Pharaoh, Thus saith Jehovah, Israel is my son, my first-born:" — Exodus 4:22 (ASV)

Israel is my son. —Compare Hosea 11:1. This tender relation, now first revealed, is not a mere metaphor, meaning “as dear to me as a son,” but a reality. The Israel of God enjoys the sonship of adoption by being taken into the True Son, and made one with Him (Romans 8:14–17).

My first-born. —Admitted to sonship in the Messiah before the other nations of the earth.