Adam Clarke on 1 Samuel 13:14

The Lord hath sought him a man after his own heart - That this man was David is sufficiently clear from the sequel. But in what sense was he a man after God's own heart? Answer:

1. In his strict attention to the law and worship of God.

2. In his admitting, in the whole of his conduct, that God was King in Israel, and that he himself was but his vicegerent.

3. In never attempting to alter any of those laws, or in the least change the Israelitish constitution.

4. In all his public official conduct he acted according to the Divine mind, and fulfilled the will of his Maker: thus was he a man after God's own heart. In reference to his private or personal moral conduct, the word is never used. This is the sense alone in which the word is used here and elsewhere; and it is unfair and wicked to put another meaning on it in order to ridicule the revelation of God, as certain infidels have done.