Exodus 4:22

And thou shall say unto Pharaoh
When arrived in Egypt, and in his presence: thus saith the Lord;
he was to declare to him that he came in his name, and by his orders, and, as an ambassador of his, required the dismission of the children of Israel out of Egypt: Israel [is] my son, [even] my firstborn;
as dear to him as a man's firstborn is, or as his only son: adoption is one of the privileges peculiar to Israel after the flesh, even national adoption, with all the external privileges appertaining to it, ( Romans 9:4 Romans 9:5 ) .