Deuteronomy - 21:15 Meaning

“If a man have two wives, one beloved, and another hated, and they have born him children, both the beloved and the hated; and if the firstborn son be hers that was hated:”

King James Version (KJV)

Matthew Henry's Concise Commentary

21:15-17 This law restrains men from disinheriting their eldest sons without just cause. The principle in this case as to children, is still binding to parents; they must give children their right without partiality.