Saul in his time as the King of Israel had no issues with David leading his army, prior to verse six; Saul had even invited David to his house and inquired that he did not return home.
Problem arose from Saul’s end when he heard the women singing Saul killed a thousand and David killed 10,000. Saul was said to have at least three emotion which deepened to envy; the first was anger, then displeasure and then suspicion of David. In most relics, this is how envy build up; first we are angry at the person then displeasure and suspicion take root.
I often wondered that if Saul was anointed how could an evil spirit, indwell him. From my understanding as the scriptures revealed that Saul tried to kill David with a Javelin (twice) but David escaped twice. In verse 12, it highlights that Saul became afraid of David because he realized that God was with and had departed from Saul.
A useful thing to see is Saul still had understanding that helped him sense the presence of God. Hence, God spirit can dwell in a man to make him sense the presence of Yahua. However, it doesn’t stop him from being inhabited if he backslides (continues in sin, doesn’t stop working iniquity)
In the next verse, Saul reduces David size of army to a 1000 out of envy and send him to the Philistines, so it would not be said that his hand killed David. This was the same ploy David used for Uriah (Barsheba’s husband) which worked because Uriah was not anointed and had no relationship with God. However, in the case of David it didn’t work.
It is important to note that immediately David sinned by killing Uriah, he immediately went in prayer saying, “Take not your spirit from me and restore unto me the joy of my salvation”, he (David questioned his integrity from that point saying “Search me and know my way, try me and know my heart and see if there is any wicked way in me to lead me to your everlasting truth.
David from experience knew he could lose God’s presence, Saul, however, knew he had lost Yahua presence but kept trying to bring another man down with him. He even unknowingly made the David fight the lord battles against the philistine of which he prevailed. Gave his daughter (Michal) as a snare to David but she loved him. Indeed, in this verse the Lord is with me is mentioned thrice, before David tells the king servant who am I?
Indeed, who are we like servant, lowly esteemed and poor (1 Samuel 18: 23) but the lord is with US?