Famine struck Israel for three years and when David inquired of the Lord concerning it, He revealed that it was because of Saul’s killing of Gibeonites.
Therefore, David went to the surviving Gibeonites, and found out what they wanted. They wanted the family of Saul killed.
However, David made an exception,
“But the king spared Mephibosheth the son of Jonathan, the son of Saul, because of the LORD’s oath that was between them, between David and Jonathan the son of Saul” (2 Samuel 21:7).
David made a promise by means of a covenant, and he kept it.
Let that be said about each of us also.