Psalms 78:70

70.And he chose David his servant. After having made mention of the temple, the prophet now proceeds to speak of the kingdom; for these two things were the chief signs of God’s choice of his ancient people, and of his favor towards them; and Christ also hath appeared as our king and priest to bring a full and perfect salvation to us. He proves that David was made king by God, who elevated him from the sheepfold, and from the keeping of cattle, to the royal throne. It serves in no small degree to magnify the grace of God, that a peasant was taken from his mean shepherd’s cot, and exalted to the dignity of a king. Nor is this grace limited to the person of David. We are taught that whatever worth there was in the children of Abraham, flowed from the fountain of God’s mercy. The whole glory and felicity of the people consisted in the kingdom and priesthood; and both these are attributed to the pure grace and good pleasure of God. And it was requisite that the commencement of the kingdom of Christ should be lowly and contemptible, that it might correspond with its type, and that God might clearly show that he did not make use of external aids in order to accomplish our salvation.