15 When a man has two wives, one loved and the other hated, and they both give him sons, but the firstborn is from the hated wife,

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.