from Martin Luther, Commentary on Galatians:
Do not despair if you feel the flesh battling against the Spirit or if you cannot make it behave. For you to follow the guidance of the Spirit in all things without interference on the part of the flesh is impossible. You are doing all you can if you resist the flesh and do not fulfill its demands.
When I was a monk I thought I was lost forever whenever I felt an evil emotion, carnal lust, wrath, hatred, or envy. I tried to quiet my conscience in many ways, but it did not work, because lust would always come back and give me no rest. I told myself: "You have permitted this and that sin, envy, impatience, and the like. Your joining this holy order has been in vain, and all your good works are good for nothing." If at that time I had understood this passage, "The flesh lusteth against the Spirit, and the Spirit against the flesh," I could have spared myself many a day of self- torment. I would have said to myself: "Martin, you will never be without sin, for you have flesh. Despair not, but resist the flesh."
I remember how Doctor Staupitz used to say to me: "I have promised God a thousand times that I would become a better man, but I never kept my promise. From now on I am not going to make any more vows. Experience has taught me that I cannot keep them. Unless God is merciful to me for Christ's sake and grants unto me a blessed departure, I shall not be able to stand before Him." His was a God-pleasing despair.