Read 2 Samuel 21 – The Bible amazes me time and time again. It all adds up like a divine mathematical equation.
Today, David avenges the Gibeonites, but to fully understand why, we need to jump back to Joshua 9! The Lord told the Israelites not to make any covenants with the locals, but these Gibeonites tricked them by dressing as if the came from a far off land. Joshua made the treaty for their safety (see Joshua 9:15).
Saul violated the treaty in his zeal to for Israel and Judah(21:2), and its up to David to right the wrongs.
Vows, oaths, treaties matter to God, even those made without consulting him. May we all be wise to be prayerful and prudent with our promises.