In Revelation 5 a mighty angel is asking who is worthy to open the scroll? One of the elders said, “The Lion of the tribe of Judah, the Root of David, has triumphed. He is able to open the scroll and its seven seals.”
David was a fighter before and after he became king. As a man after God's own heart, he kept loving, obeying and trusting God his whole life (except for Bathsheba).
Don't get discouraged if you are always in a battle!