16 Then when he gives his property to his sons for their heritage, he is not to put the son of his loved one in the place of the first son, the son of the hated wife:

Matthew Henry's Commentary on Deuteronomy 21:16

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.