Deuteronomy 21:15 - Meaning and Application

This law keeps men from taking away the birthright of their oldest sons just because they feel like it, or without a real reason.

The case described here is very helpful. It shows the trouble that comes from having more than one wife, something the law of Moses did not stop, likely because people would eventually see its bad effects in their own homes. The situation assumed here is this: if a man has two wives, one will almost always be loved more than the other, as Jacob loved Rachel more than Leah. That kind of favoritism leads to quarrels, jealousy, envy, confusion, and every kind of wrong. It brings lasting unhappiness and trouble to the husband as well as sin into the family. Those who follow God’s law do far better for their peace and contentment than those who give in to their own desires.

This also shows how God often supports the weaker side and gives more honor to the one that seems to have less. Here the first-born son is assumed to belong to the wife who is less loved. That was true in Jacob’s family, since “the Lord saw that Leah was hated” (Genesis 29:31). God, who wisely provides for every household, gives each person their share of comfort. If one wife has the honor of being the beloved, the other may have the honor of bearing the firstborn son.

This law still teaches parents today to give their children what belongs to them, without favoritism. In the situation described, the oldest son, even if he is the son of the less loved wife, must receive his birthright, which meant a double share of the father’s property. He is called “the beginning of his strength,” because in him the father’s family begins to grow stronger, and his household begins to be filled like a man’s quiver filled with arrows (Psalm 127:4). So the right of the firstborn belongs to him (Deuteronomy 21:16, 17).

Jacob did take Reuben’s birthright and give it to Joseph, but he did so because Reuben had lost it through his sin with his father’s concubine, not because he was the son of the less loved wife. This matters, so that no one would use Jacob’s act as a reason to do the same thing wrongly. When a father makes his will, or otherwise divides his estate, he must not treat a child worse because of the mother’s low place in the family, since that was no fault of the child.

Parents should make no other difference in how they treat their children than the difference they clearly see God making in giving grace to them. And since it is God’s providence that makes heirs, we must accept his ordering in such matters and not resist it. No father should cast off a son until it is plainly shown that God has cast him off, and that is hard to say of any son while he is still alive.