In II Chronicles 6, King Solomon is dedicating the newly-built Temple.
In vv 4-6, we read (in the KJV):
4 And [Solomon] said, Blessed be the LORD God of Israel, who hath with his hands fulfilled that which he spake with his mouth to my father David, saying,
5 Since the day that I brought forth my people out of the land of Egypt I chose no city among all the tribes of Israel to build an house in, that my name might be there; neither chose I any man to be a ruler over my people Israel:
6 But I have chosen Jerusalem, that my name might be there; and have chosen David to be over my people Israel.
God said that God did not choose a man to rule over Israel prior to King David? What about King Saul, whom God chose to be king, and whose reign was prior to that of David?
Various interpreters say that God did not technically choose Saul to be king. The Orthodox Jewish Artscroll commentary notes that God long before the time of Saul planned for the king of Israel to come from Judah, not another tribe (Genesis 49:10). David was from Judah, whereas Saul was from Benjamin. According to the Artscroll, God intended from the outset for Saul’s reign to be temporary. Jimmy Swaggart says that God intended David’s line to be permanent and for all future kings of Israel to come from that line. For Swaggart, when II Chronicles 6:5-6 says that God chose David and no one else prior to him, the idea is that God chose David’s line to have permanent rulership over Israel. E.W. Bullinger notes that God “overruled the choice of the people” and cites I Samuel 8:5 I do not entirely understand what Bullinger was getting at, but perhaps he was saying that God in choosing Saul as king was simply giving in to the people’s demands for a king, whereas God in choosing David was making God’s real choice. Saul did botch some things up as king: maybe God foresaw this and set up Saul to punish the people of Israel for their request, which offended God.
I Samuel 13:13-14 may be relevant to this discussion. The context here is Saul’s disobedience to God in offering sacrifices himself rather than waiting for Samuel the prophet to come. “And Samuel said to Saul, Thou hast done foolishly: thou hast not kept the commandment of the LORD thy God, which he commanded thee: for now would the LORD have established thy kingdom upon Israel for ever. But now thy kingdom shall not continue: the LORD hath sought him a man after his own heart, and the LORD hath commanded him to be captain over his people, because thou hast not kept that which the LORD commanded thee.” Notice that God would have established Saul’s kingdom forever, had Saul not disobeyed. On the one hand, that seems to challenge the idea that God intended Saul’s reign from the outset to be temporary. On the other hand, maybe God knew ahead of time that Saul would disobey God and thereby forfeit an eternal reign for his line, and thus God did plan for Saul’s reign to be temporary. In any case, the passage says that David was a man after God’s own heart: that could mean that David was God’s real choice, that David genuinely had the qualities that God desired a king of Israel to have.
Keil-Delitzsch simply note that the part of II Chronicles 6 about God not choosing a ruler over Israel prior to David is not in I Kings 8, which presents Solomon giving the same sort of speech at the Temple as what is in II Chronicles 6. That could mean that the Chronicler himself is contributing the part about God not picking a king prior to David to rule Israel. But the Chronicler was aware of King Saul (I Chronicles 5:8-13). Why, then, would the Chronicler say that God did not choose a king of Israel prior to David?
A possible explanation could be that from the beginning (or, at least, from the time of Jacob’s son Judah) God planned for the king of Israel to descend from Judah, and so, technically, God chose David to be king long before he chose Saul. I Chronicles 5:2 states: “For Judah prevailed above his brethren, and of him came the chief ruler…” My problem with this explanation is that II Chronicles 6:4 states that God did not choose a ruler over Israel since the time of the Exodus, until David came along. The idea there seems to be that God chose David when David came along, not several centuries before David was born. I also have a slight problem with the proposal that God uniquely chose David because David’s line was to be permanent. So often in Chronicles, the duration of the reign of David’s line seems to be contingent on its obedience to God’s commandments, which is technically not permanence. But perhaps there are ways to get around that: that the reigns of certain Davidic kings may be overthrown for disobedience while the line itself still reigns forever, or that God will one day restore the line of David to the throne.
I do not know why the Chronicler said what he said in II Chronicles 6:5-6, but perhaps it is a combination of the explanations others have offered: that David was God’s real choice to be king, whereas Saul really was not. The Chronicler does exalt David a lot.