The believer’s guarantee of victory is in taking on the battles of life in a representative capacity knowing that the battle is the Lords and allowing the Lord to fight the battle. In this sense the believer only comes to battle in the name of the Lord.
“Then said David to the Philistine, Thou comest to me with a sword, and with a spear, and with a shield: but I come to thee in the name of the LORD of hosts, the God of the armies of Israel, whom thou hast defied. This day will the LORD deliver thee into mine hand; and I will smite thee, and take thine head from thee; and I will give the carcases of the host of the Philistines this day unto the fowls of the air, and to the wild beasts of the earth; that all the earth may know that there is a God in Israel.” 1 Samuel 17:45-46
David understood this principle very well and that was the reason he never lost a single battle. Every battle was the Lords battle, he never proved himself as a warrior. He would even consult the Lord in very obvious situations where he should have jumped into action. The name of the Lord is the Lords badge of honour and anyone who understands how to put it on the line can never suffer defeat.