1 Samuel 16:3
And call Jesse to the sacrifice, and I will shew thee what thou shalt do: and thou shalt anoint unto me him whom I name unto thee. And call Jesse to the sacrifice, and I will shew thee what thou shalt do: and thou shalt anoint unto me him whom I name unto thee.
God told Samuel to stop mourning for Saul because Saul had been rejected from reigning over Israel, and sent him to Jesse the Bethlehemite because He had provided Himself a king among Jesse's sons. Samuel was to fill his horn with oil and go, taking a heifer with him, saying he had come to sacrifice to the Lord. He was to call Jesse to the sacrifice, with God promising to show him what he should do, and he was to anoint unto God only the one whom God would name to him.
Samuel obeyed and came to Bethlehem, where the elders trembled at his coming and asked whether he came peaceably, and he answered peaceably. They accepted the invitation to the sacrifice, and Samuel called Jesse and his sons also, the altar was built and the sacrifice made ready, and all of Jesse's household was present except David the youngest son. David had been left to guard the sheep, because it was not safe to leave the flocks unprotected. The choice of king was not to be made by outward appearance, so Eliab's stature and dignified looks did not make him fit to rule.
God guided Samuel to David, Jesse's youngest son, choosing and appointing him at Bethlehem to succeed Saul on the throne of Israel, as part of the account of David's early life and anointing. This divine choice meant David was chosen by the Lord to reign over Israel, was qualified to bear the responsibilities of the kingdom, and did not sit upon a traitor's throne. His faithful and courageous service as a shepherd prepared him to lead God's people, and he would in time exchange the shepherd's crook for a scepter.
Though utterly helpless in himself, David as a shepherd lad holding God's promise of the throne trusted God's word and stood by faith against Saul, the established monarch determined to hold fast his power. His stand proves that faith in God's word withstands the power of the whole world and belongs to the world's true nobility and royal line in which the youth of today are called to take their places. Although Abner, Saul's commander-in-chief, knew of God's choice, ambition and unprincipled character, hatred increased by David's rebuke, and unwillingness that Jesse's son should succeed Saul led him to despise God's chosen man and raise up Ishbosheth in division against him.