Deuteronomy 21:15-17, God Breaks the Law
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: Then it shall be, when he maketh his sons to inherit that which he hath, that he may not make the son of the beloved firstborn before the son of the hated, which is indeed the firstborn: But he shall acknowledge the son of the hated for the firstborn, by giving him a double portion of all that he hath: for he is the beginning of his strength; the right of the firstborn is his.
//This interesting law was apparently established to protect the true firstborn’s inheritance. The firstborn was to receive a double portion in his inheritance. Even if a man’s first son comes from a wife that he hates, he must give that son preference.
But doesn’t this precisely describe the situation with Abraham, Isaac and Ishmael? God tells Abraham to send the first-born Ishmael and his mother away into the desert, with nothing but a skin of water, and to give everything to Isaac instead.
In fact, how many more pairs of brothers can you think of where the firstborn is snubbed for a later child, with the favor of God? Here are some more non-firstborns who won God’s approval: Abel, Jacob, Gideon.
Indeed, both the priesthood (Eleazar, Ithamar, Levi) and the kingship of Israel (David, Solomon, Judah) are founded on non-firstborns.
Where did this law come from, if not even God pays it any mind?