1 Samuel 20:31

As long as the son of Jesse liveth, &c.— But how did Saul know, that, as long as the son of Jesse lived, Jonathan should not be established, nor his kingdom? If it was all jealousy and surmise, his ordering him to be brought to be put to death was unreasonable and wicked, and can be justified upon no principles of justice and humanity. If Saul knew that as himself was rejected, David was really anointed to succeed him by Samuel, at God's command, his ordering him to be put to death was both impertinent and wicked: for he knew that David had then as good a right to succeed him, in preference to Jonathan, as he himself had of obtaining the throne in preference to every other man of Israel; and, therefore, that he ought not to destroy the man whom God had appointed to succeed him, and with all his endeavours would not be able to do it if God had determined to make him captain over Israel. So that in whatever view we consider this reply of Saul, fetch him,—for he shall surely die, it will appear to be absolutely improper, and that it could proceed from nothing but the incurable inveteracy of a disordered mind, agitated by ambition, jealousy, and an implacable desire of revenge. He shall surely die, is, in the Hebrew הוא בןאּמות ben muvet hu, he is the son of death; a Hebrew form of speaking, which denotes either a man worthy of death, or devoted to death.