Psalms 89:20

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.