Question: In 1 Samuel 13:13 Samuel tells king Saul that if he had obeyed Yahweh, Yahweh would have established his kingdom forever. But this can’t be true. Saul was a Benjamite, and the prophecy of Jacob in Genesis 49:10 is that the kingship will not depart from the line of Judah, a prophecy that came hundreds of years before Samuel and Saul. Didn’t Samuel know the prophecy that the kingship would go through Judah? It seems the only possibilities are that Samuel either a) believes Saul would have kept the kingship if he had trusted God, which means Samuel didn’t know the prophecy, or b) knows the prophecy and lies or just gives an inaccurate statement or even guilt trip.
Answer: Let’s suppose that Samuel did not know the prophecy of Genesis 49. We must still answer the question of whether Samuel is speaking to Saul out of his own wisdom or prophetically as he has heard from God? We might wonder about the first statement, that God would have established Saul’s kingdom forever, but we would certainly see his next statement as coming from God and true, that God was looking for someone after His own heart. This suggests that Samuel was speaking for God and not out of his own knowledge (or lack thereof). This would mean that if anyone was wrong about anything it was God who was wrong to tell Samuel that He would have established Saul’s kingdom forever had Saul obeyed. So it doesn’t matter if Samuel knew of Genesis 49 or not. He was repeating Yahweh, and certainly Yahweh knew the prophecy of Genesis 49.
So how do we resolve this? God knew that Saul was not going to succeed at obeying, yet nevertheless was willing to offer him the kingdom forever if he did. There had to be a genuine option for Saul to have the kingdom if he obeyed. It wasn’t a guilt trip but necessary knowledge to have for himself and for subsequent contenders for the throne. But God was also wanting to show Israel that the character of their king was crucial to their welfare as a nation. In His decree He purposed to remove Saul and install David, thus fulfilling the prophetic word He gave to Jacob/Israel.
Samuel is not a liar because he is simply telling Saul what God told him to tell him. Even if Samuel knows the prophecy of Genesis 49, which I would suppose he did, he also knows that God is looking at things from His eternal perspective and making a genuine offer to Saul (which I am also assuming was clear on the front end), nevertheless knowing that Saul would not/could not make good on it. His prophecy through Jacob came true in a circuitous route. The reason ultimately for this route is known only to God, but we can see the fringes of His purposes as described above.
We see something similar in Acts 27 with Paul on the ship to Rome. God tells him that not a life will be lost during the storm, only the ship. But when the sailors try to escape the ship he tells the Centurion that unless they are stopped those on board will be lost. God knew that Paul’s warning would be heeded and predicted that none would perish.
Follow up question: If Samuel is speaking prophetically in 13:13-14, in order to preserve God and Samuel’s integrity, I am forced to say God must’ve offered a real possible outcome to Saul – obey and have the kingship for all time. As for how He would have dealt with fulfilling the Genesis 49 prophecy WHILE Saul’s lineage retained the kingdom, God would’ve had to get creative. Perhaps Saul’s daughter would’ve married a Judahite, producing a son in both Saul’s lineage and Judah’s lineage to become king. Who knows? But I am satisfied in believing that God could have, and WOULD have, found a creative solution to fulfill both prophecies. What do you think of that possibility?
Follow up answer: I think it is an admirable possibility.