15 "Suppose a man has two wives, but he loves one and not the other, and both have given him sons. And suppose the firstborn son is the son of the wife he does not love.

Matthew Henry's Commentary on Deuteronomy 21:15

Commentary on Deuteronomy 21:15-17

(Read Deuteronomy 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.