One of the strange things about the Old Testament from a modern perspective is the law of primogeniture. Primogeniture is the English word derived from the Greek word for the Hebrew word for "firstborn." (Follow that?) The law of the firstborn refers specifically to the exclusive right of the firstborn male to the inheritance of the family.
At first glance, the law seems arbitrary and filled with potential abuse and lacking in good dose of pragmatic wisdom. So we should ask some questions and try to determine what might behind God infusing this Oriental custom with the sanction of His Spirit (see, Gen. 10:15; 21:10; 25:13; 36:15; Dt. 21:17 and the contexts surrounding them).
Why might God do this? Wouldn't this inevitably result in times when a less or even least worthy son would be leading the family? Wouldn't this produce all manner of inequities at times both for more talented, faithful or worthy and honorable sons, to say nothing of talented and worthy daughters? And what about the surviving wife? Doesn't she have a say in who should best lead the family fortune?
We know that this law of primogeniture was not absolute. God on numerous ocassions and fathers in a number of others, chose different sons than the first born. For example Judah was not the first born of Jacob, Reuben was. Jacob was not the first born of Isaac, Esau was. David is the eighth born son of Jessi and going back to Judah, Joseph was the probably the most worthy and talented son in the family of Jacob.
So why does God endorse the law of primogeniture in general. A mystical Jewish response is that God saw to it that the "right one" always got the rights. (I know this because I called up a Rabbi and asked.) Well this is no doubt true in the grand and eternal view of history, nevertheless, one can't help but think that numerous times a father would die, and his least worthy or talented son would become the leader of the clan when a more suitable son was passed over just because he was younger. Why?
I don't know and neither does anyone else. But perhaps part of the answer is that God is far more interested that his people learn to trust HIM then anything else. He doesn't want us to trust people, procedures, family or even law. God wants His people to trust what He says, independent of whether it looks fair, wise or just. He wants His people to place their highest value on the words of His lips, on the plan and character of a good and gracious God rather than on the momentary appearance of what looks pragmatically best in a situation.
"Is that why LORD? Teach me oh God. Teach me. Help me to trust the words of your mouth more than what I think seems right. Amen"