Saul sent for the renown man of music and valor David to play the lyre whenever God's harmful spirit tormented him, causing the spirit to flee. Saul came to love David so much, that he made him his armor-bearer and asked Jesse for his position to be made permanent. (1 Samuel 16:14-23)
David went back and forth from Saul to feed his father's sheep at Bethlehem while Israel was campeed in the Valley of Elah against the Philistines camped between Socoh and Azekah in Ephes-dammim. Jesse sent David with an ephah of parched grain and ten loaves of bread to his three oldest brothers, Eliab, Abinadab, and Shammah, and ten cheeses to their commander. David arrived and left everything with the baggage keeper and met his brothers. Goliath of Gath came out and challenged Israel, so David asked who the uncircumcised Philistine was to challenge the army of the living God. Saul sent for him, and David convinced him to let him fight, since the LORD already delivers him from lions and bears. He rejected Saul's armor and sword, though, equipping a staff, a sling, and five stones from the brook. Goliath asked if he was a dog to be approached with a stick, and David said the LORD saves not with sword and spear. David's first stone killed him, and he cut his head with Goliath's own sword. He returned to Jerusalem, and Abner brought him to Saul, giant's head in hand. Saul asked his father's name, though he had known it previously. (1 Samuel 17)
David joins Saul's royal family
Immediately, Jonathan loved him. Saul took him and didn't allow him to return to Jesse's house. Jonathan made a covenant, gave him his robe, his armor, his sword, his bow, and his belt. David was placed over Saul's men of war, seeing success and popularity with the people and Saul's servants. The nation's women sang Saul struck down thousands and David ten thousands. Saul raved later, so David played his lyre day by day, but Saul hurled the spear in his hand at him. David evaded twice. Saul removed him and set him as commander of a thousand, so he went out and came in before the people and found success and love from his country.
Saul offered Merab in marriage, but David downplayed his eligibility to become son-in-law to the king. She was given to Adriel the Meholathite when David should have received her. Michal loved him, so Saul offered her and had his servants convince him to become son-in-law. David refused the honor on grounds of his poverty and reputation. But when they told him Saul wanted no bride-price but a hundred Philistine foreskins, it pleased him. David brought double, receiving Michal. And David had more success against the princes of the Philistines than all servants of Saul, so his name was highly esteemed.
Jonathan warns David that Saul seeks to kill him and to hide. Jonathan returned and reported that Saul has sworn not to put David to death and brought him back to Saul's presence as before. (1 Samuel 19)
Questions
Why did Saul ask David's house? He is the one who wrote to Jesse for David in the first place.
Matthew Henry supposes Saul thought little of him and notes the stalemate between Israel and Goliath's camp was going on for 40 days while David was spending significant time caring for his father's flock in Bethlehem. (1 Samuel 17:15)