"The LORD said to Samuel, How long will you mourn for Saul, seeing that I have rejected him ... ? I will send you to Jesse the Bethlehemite ; for I have seen among his sons a king for me ... the LORD does not look what the man is looking at, for the man looks to the outward appearance, and the LORD looketh to the heart." 1 Samuel 16 1, 7
Saul is the first king of Israel, in the eleventh century BC But he is not concerned with obeying God. God can not count on him to lead the people and he invites the prophet Samuel to anoint a king whom he himself has chosen, one of the sons of Jesse.
Samuel obeyed the Lord and went to meet the family of Jesse. The law reserved the firstborn of a family to Jehovah ; Samuel therefore thinks that the eldest of the family will be chosen (17:13) : "And he saw Eliab, and said, Surely the anointed of Jehovah is before him" (v. 6). In fact the choice of the LORD is not on the eldest Eliab, but on the youngest in the family, David, who "feeds the flock" (v. 11). When he presents himself, the LORD said to Samuel : "Arise, anoint him ; for this is he" (v.12). Why this choice ? The author of the book states: "The Lord looks to the heart" and not to appearance, not to social rank. That's part of his power : for him, nothing is hidden. The heart represents for the Jews the center of being, the source of choices and thoughts.
David is young ; it makes him more fit to be formed by God. He lived near God. He found his pleasure and strength in God ; he sings psalms and kills the lion and the bear. His activity as a shepherd will make David this pastor concerned with the good for his people.
David will remain throughout the political history of the people the reference of the king according to the heart of God. True, he has fallen several times ; but he never betrayed God by worshiping idols.
Formulas recur regularly throughout the two books of Kings : "Solomon ... did not fully follow the Lord like David his father" (1 Kings 11: 6) ; but Josiah "did that which was right in the sight of the LORD, and walked in all the ways of David his father" (2 Kings 22: 2).
The example of David encourages me : if I am faithful in the little things and ready to let myself be formed by God, he will not fail to show me his confidence.
Source (Pleasing the Lord)