So David marched out and prospered in everything Saul sent him to do, and Saul set him over the men of war. And this was pleasing in the sight of all the people, and of Saul’s officers as well.
David was anointed to the crown to take it out of Saul's hand, and over Jonathan's head, and yet here we find, I. That Saul, who was now in possession of the crown, reposed a confidence in him, God so ordering it, that he might by his preferment at court be prepared for future service.
Commenting on 1 Samuel 18:1-5
And David went out whithersoever Saul sent him,.... About any business whatsoever, especially about martial affairs, for which he was abundantly qualified: and behaved himself wisely; in the management of them, using great prudence and discretion, and so failed not of success, and of recommending himself; the Targum renders it "prospering"; he was prosperous and successful in whatsoever he engaged, for the Lord was with...
And David went out whithersoever Saul sent him, [and] behaved himself wisely: and Saul set him over the men of war, and he was accepted in the sight of all the people, and also in the sight of Saul's servants. (b) That is, he prospered in all his doings.