“And how shall I make atonement, that you may bless the heritage of the LORD?" (21:3). Though to us it is unfair and barbaric, in ancient cultures, it would have made sense that Saul’s grandsons could “atone” for his acts by their deaths. King Saul had broken a treaty by slaughtering the Gibeonites (21:2), and because he was a king who represented all the people of Israel, the consequences hung over the nation like a curse (v1). The deaths of seven innocent men broke the curse (21:14).
Our loving God went beyond either ancient or modern ideas of justice, choosing mercy, when he sent his Son to represent the entire human family and atone for our sins.