The LORD shall fight for you, and you shall hold your peace. Exodus 14:14
Ye shall not fear them: for the LORD your God he shall fight for you. Debt 3:22
There are many instances in the bible where God reminds us that we are not to fight for ourselves but He will fight for us. When someone does us wrong it is not our responsibility to take vengeance. Romans 12:19-21 states it so clearly. Even our inner battles should be fought by God. Letting God fight your battles does not mean that you can sit back and relax though, it requires trust and faith; knowing that everything will work out for your good. The victory is already won if you just believe.