John Wesley on 1 Samuel 16:1

Mourn - And pray for his restitution, which the following words imply he did. Oil - Which was used in the inauguration of kings. But here it is used in the designation of a king; for David was not actually made king by it, but still remained a subject. And the reason of this anticipation was the comfort of Samuel, and other good men, against their fears in case of Saul's death, and the assurance of David's title, which otherwise would have been doubtful. I have provided - This phrase is very emphatical, and implies the difference between this and the former king. Saul was a king of the people's providing, he was the product of their sinful desires: but this is a king of my own providing, to fulfil all my will, and to serve my glory.