'Battles of the Lord' in the Bible

Then Saul said to David, "Here's my oldest daughter, Merab. I want to give her to you in marriage. Only be a brave warrior for me and fight the battles of the Lord." For Saul thought, "There's no need for me to raise my hand against him. Let it be the hand of the Philistines!"

Please forgive the sin of your servant, for the Lord will certainly establish the house of my lord, because my lord fights the battles of the Lord. May no evil be found in you all your days!