v1: Samuel had anointed Saul, and now mourned for him, as he slid further away from the Lord God. But the Scriptures and the promises of God had to be fulfilled, see 15.28. A new king had to be found, and Samuel had the task of anointing him. The Lord God directed Samuel to Bethlehem, and to the family of Jesse. The Lord also directed how Samuel would bring the people together (v3).
v2-4: Samuel recognised Saul's potential jealousy, for he would not tolerate a rival king. So, Samuel's life would be at risk. The elders of Bethlehem also realised this.
v5: The elders of Bethlehem were worried. Samuel had indeed come to sacrifice, and the elders of Bethlehem were invited.
v6: Eliab, like Saul, had an impressive appearance.
v7: God looked at Eliab's heart; this was the standard by which Saul had been rejected (13.13-14), and by which David would be accepted. Men judge the heart by actions; God judges our actions by the heart.
Even Samuel nearly erred here; but his ear was open to God's voice of correction. We need to see as the Lord sees; the spiritual reality is sometimes different from the physical appearance.
v8-11: Jesse had all his sons brought before Samuel. David had not even been invited. He was being faithful in tending the sheep. He was taken from the sheepfolds to feed the flock of God, and to Shepherd His people.
v12-13: David was chosen and appointed, by God and by Samuel, and in public.
These events in Bethlehem were unknown to Saul. Thus, when David served Saul, he was ignorant of the fact that David had been anointed as king.
v14: The narrative contrasts the blessing of the Spirit of God upon David, with the evil spirit upon Saul. (It is possible that this incident preceded David's anointing.)
v15-17: It was recognised that music would have an effect upon the torment of the evil spirit, see v23.
v18: David's good reputation among the people. He was a young man, but godly; age is no barrier to godliness.
v19-20: See 14.52; Saul took David for himself.
v21-23: Saul as impressed with David; he later gave more responsibility to David, as his armour-bearer. Again we see that David proved faithful in whatever task he was given. Later, Saul became jealous of David's success, 18.8