Then said Abishai to David, God has delivered up your enemy into your hand this day: now therefore please let me strike him with the spear to the earth at one stroke, and I will not strike him the second time.
Saul underneath knew that someday David was gonna take the throne. He was trying to protect the throne and to pass it onto his own children. But yet in his heart, he knew that God had anointed David, and that David was God's anointed king. "Then Saul said to David, Blessed be thou, my son David: thou shalt both do great things, and still prevail."