1 Samuel 22:17
And the king said unto the footmen that stood about him, Turn, and slay the priests of the LORD; because their hand also is with David, and because they knew when he fled, and did not shew it to me. But the servants of the king would not put forth their hand to fall upon the priests of the LORD.
This command belongs to the time after David slew Goliath, when Saul kept David with him and would not permit him to return to his father's house. At that time the soul of Jonathan was knit with the soul of David and Jonathan loved him as his own soul, so they made a covenant to be united as brethren. Jonathan gave David his robe and his garments even to his sword and bow and girdle, while David was entrusted with important responsibilities and yet preserved modesty and won the affection of the people and the royal household.
The order to kill was given in maddened rage after David escaped Saul's plan to capture him at Adullam. Saul believed traitors in his camp had warned David of his danger. He charged his counselors with conspiracy against him and tried to bribe them with rich gifts and honor to betray David's friends.
Doeg the Edomite then informed on David's visit to Ahimelech and misrepresented it so as to kindle Saul's anger against the man of God. He was moved by ambition and avarice and by hatred of the priest who had reproved his sins.
Saul decreed that the whole family of the priest should perish, ordering his footmen standing about him to turn and slay the priests of the Lord because their hand was also with David and because they knew when he fled and did not show it to him. The decree was executed by the murderous hand of Doeg upon Ahimelech and eighty-five persons who wore a linen ephod, and ruin was then brought upon Nob.
The act was done without any command from God, under the control and guidance of Satan. It exposes the perversity of the human heart that has refused the guidance of God. The same Saul had thought himself too compassionate to execute God's sentence to destroy the Amalekites utterly when their iniquity was full, and had spared what was devoted to destruction, yet he could now slay the priests of the Lord.