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Thy blood be upon thy head - If he killed Saul, as he said he did, then he deserved death; at that time it was not known to the contrary, and this man was executed on his own confession.

David might well think his sentence just though severe, for he had more than once expressed the deliberate opinion that none could lift up his hand against the Lord‘s anointed, and be guiltless (see 1 Samuel 24:6; 1 Samuel 26:9, 1 Samuel 26:11, 1 Samuel 26:16).

David was sincere in his mourning for Saul; and all with him humbled themselves under the hand of God, laid so heavily upon Israel by this defeat. The man who brought the tidings, David put to death, as a murderer of his prince. David herein did not do unjustly; the Amalekite confessed the crime. If he did as he said, he deserved to die for treason; and his lying to David, if indeed it were a lie, proved, as sooner or later that sin will prove, lying against himself. Hereby David showed himself zealous for public justice, without regard to his own private interest.