I Chronicles - Chapter 12
The David Fan Club - Tziklag Chapter
This chapter enumerates various groups that supported David before he became accepted as king; it has no parallel account in the Books of Samuel.
First, the chapter lists those who joined with David at Tziklag, during his oppression by Saul. These included mighty warriors from Saul's own Tribe of Benjamin. They were joined by soldiers from the Tribe of Gad, whose prowess is favorably compared to a lion's. We are told that the least competent of the Gadite leaders was as good as 100 soldiers and that the best among them was comparable to 1,000 soldiers. They were the ones who crossed the Jordan and put all the residents to flight.
David was later joined by more supporters from Benjamin and his own Tribe of Judah. David told the new arrivals that he would welcome their help, but if they intend to betray him to Saul, then G-d knows he is innocent and will judge. The leader, a man named Amasi, spoke for the group, that they offered their help in good faith. David accepted them and gave them important roles among his forces.
In I Samuel 28-29, David feigns an alliance with the Philistines, but they send his forces home because many of them are rightly suspicious of his sincerity. We are told here that at that time, forces from the Tribe of Menashe joined up with David, helping him with his battle against the Amalekites and earning their places in his forces. Every day, more and more people joined David until his camp had become a most impressive size. (Verse 23 calls it "a camp to G-d," but that just means something very large. For example, Jonah 3:3 calls Nineveh a "great city to G-d.")
Next, the chapter lists the leaders of the various Tribes, who came to Hebron to crown David king after Saul. We are given counts for each Tribe, plus the kohanim (priests). (David's own Tribe of Judah was actually under-represented, as he had been ruling over them for seven years by that point.) We are also told that Tzadok, an important person who would later become High Priest, brought 22 princes who were members of his family.
In passing, we are given details about the various Tribes. For example, the people of Benjamin had supported Saul to the very end (not surprising), while those of Ephraim were skilled warriors. Most striking, perhaps, is that the people of Issachar are called "those who know understanding and the times." The exact meaning is obscure, but "Rashi" says that members of the Tribe of Issachar were among David's most prominent advisors. Indeed, the Tribe of Issachar was renowned for their Torah knowledge, pursuant to their blessing from Jacob in Genesis 49.
Representatives from all the Tribes came to Hebron and unanimously crowned David king. They celebrated the event for three days, with food the people of Hebron and several of the Tribes had provided for the occasion.