The hard part for me is that we can never totally win against this enemy. And then I start to wonder why God has us fighting a loosing battle. But God has His reasons and I don't need to understand them. All I have to is know is He calls us to war, even if we can never win. I once read somewhere, "We are free to struggle, but we’re not struggling to be free".
We must battle our sin until we are freed from this earth, where we can't be dragged down by own flesh. Then our soul, washed clean by the blood of the Lamb, can share in the victory, rejoicing at the Heavenly throne. And you know what? I bet it will will be worth it and then some.
So for here on Earth, it's not in the winning, but in the fighting.
For we know that the law is spiritual, but I am carnal, sold under sin. For what I am doing, I do not understand. For what I will to do, that I do not practice; but what I hate, that I do. If, then, I do what I will not to do, I agree with the law that it is good. But now, it is no longer I who do it, but sin that dwells in me. For I know that in me (that is, in my flesh) nothing good dwells; for to will is present with me, but how to perform what is good I do not find. For the good that I will to do, I do not do; but the evil I will not to do, that I practice. Now if I do what I will not to do, it is no longer I who do it, but sin that dwells in me. I find then a law, that evil is present with me, the one who wills to do good. For I delight in the law of God according to the inward man. But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members. O wretched man that I am! Who will deliver me from this body of death? I thank God—through Jesus Christ our Lord!
Romans 7:14-25 NKJ
Fight, my dear brothers and sisters, and when you grow weary, think of the cross, and you will find His strength.