1 Samuel 16:1
And the LORD said unto Samuel, How long wilt thou mourn for Saul, seeing I have rejected him from reigning over Israel? fill thine horn with oil, and go, I will send thee to Jesse the Beth-lehemite: for I have provided me a king among his sons.
God had rejected Saul from reigning over Israel and told Samuel to stop mourning for him. God commanded Samuel to fill his horn with oil and go to Jesse the Bethlehemite, because He had provided Himself a king among Jesse's sons, choosing David to be anointed and to rule in Saul's place. God further directed Samuel to take a heifer, to say he had come to sacrifice to the Lord, to call Jesse to the sacrifice, and to wait to be shown what to do and anoint the one God would name. Samuel obeyed and came to Bethlehem, where the elders trembled at his coming and asked if he came peaceably and he answered peaceably, the invitation was accepted, the altar was built and the sacrifice made ready, while David the youngest was left to guard the sheep because it was not safe to leave the flocks unprotected.
David was then still a boy, the youngest son of Jesse, living in retirement as a humble shepherd on the hills around Bethlehem a few miles south of Jerusalem in a hill-dwelling home in the hill country, watching his flocks, singing songs of his own composing and playing his harp, already chosen by God and being prepared in that solitary life for the work to be committed to him in after years. His early life there had the Hebrew home training that brought Israelite youth forth vigorous in body and mind, quick to perceive and strong to act, with the heart prepared like good ground for the precious seed and the mind trained to see God in revelation and nature. The stars, trees and flowers, lofty mountains and babbling brooks spoke to him and the voices of the prophets met a response in his heart, the same training as Moses in Goshen, Samuel by Hannah, Daniel before the captivity, Christ at Nazareth, and Timothy by Eunice and Lois.
Human judgment cannot choose God's anointed because it looks on outward appearance and stature while the Lord looks on the heart, so God refused the noble-looking elder sons and chose David the youngest, a mere youth called from the field, and no one can tell by looks which youth will prove most promising and render the best service. God thereby promised David the throne while he was still a shepherd lad and Saul remained the established monarch determined to hold fast his power, and though utterly helpless in himself David trusted God's promise despite his apparent helplessness before Saul. His stand against Saul witnesses to the power of God's word against human power and policy in support of evil, showing that trust in God's promise can withstand human power, and marks him among the world's true nobility and royal line in which youth today are called to take their places.
David was the man God had appointed to the throne, though Saul's former commander Abner resisted his succession and sought to advance Saul's house for his own ambition. Therefore selecting only a few for thorough training is wrong, and all children and youth need general education and training in schools so they may be fitted for usefulness, qualified for places of responsibility, and inspired to become laborers together with God.