How soon do unholy hearts lose the good impressions convictions have made upon them! How helpless were Saul and all his men! All as though disarmed and chained, yet nothing is done to them; they are only asleep. How easily can God weaken the strongest, befool the wisest, and baffle the most watchful! David still resolved to wait till God thought fit to avenge him on Saul. He will by no means force his way to the promised crown by any wrong methods. The temptation was very strong; but if he yielded, he would sin against God, therefore he resisted the temptation, and trusted God with the event.
SDA Bible Commentary (limited)
Volume 1-7
11. The spear. David was keenly alive to the need of securing material evidence of his attitude toward Saul. While expecting God to do great things for him, he knew that he too had a part to act in the present situation.