Psalms 89:20

I have found David my servant - This is the sum of what God had said in prophetic visions to his saints or holy persons, Samuel, Nathan, and Gad; see 1 Samuel 16:1, 1 Samuel 16:12. Here the psalmist begins to reason with God relative to David, his posterity, and the perpetuity of his kingdom; which promises appear now to have utterly failed, as the throne had been overturned, and all the people carried into captivity. But all these things may have reference to Christ and his kingdom; for we are assured that David was a type of the Messiah.

I have found David my servant - That is, I found him among the sheepfolds; in humble life. I saw there one who was qualified for the high office of being the ruler of the nation, and I designated, or set him apart, for that office. The idea is, that there was in him a precious qualification for this work, and that God had seen this, and, in accordance with this, had summoned him to his service.

With my holy oil have I anointed him - By the hand of Samuel. 1 Samuel 16:13. Oil was used in setting apart prophets, priests, and kings. It was poured upon the person - emblematic of the pouring out upon him of wisdom and grace from on high to qualify him for his office.