Galatians 5:17 tells us that the flesh fights against the spirit and the spirit against the flesh. This is because our flesh is not reborn when we accept Jesus Christ as our Savior. Our spirits are reborn. The fleshly attitudes in us are against God and will never be subjected to him. The fleshly way is against God and the flesh can never be subjected to God's way, love or law. (Romans 8:7) I know that when I am disappointed in God, unhappy with him and not appreciating and respecting him, I am walking in my flesh.
My reborn spirit loves God with a perfect love. The more that I walk in the spiritual life, or in the spirit, the more that I am happy and satisfied with God. This knowledge and revelation helps me to quickly get back into my reborn spirit side of my being, with the help of the Holy Spirit, when my thoughts and feelings are not helpful or fair. It is difficult to resist the fleshly way of thinking because we are born into it. We always need the help of God's Spirit in us to get back into our reborn spirit's way of functioning.
While on this earth, we as Christians have our reborn spirits and we still live in bodies that function by fleshly control. The best that we can do with our flesh is to crucify and bring it under. (Galatians 5:24, I Corinthians 9:27) Doing that with that same flesh, however, does not have lasting effects. The flesh, any way that you cut and dry it, profits us nothing. That's why we fall back into our detrimental habits and destructive ways when we try to make ourselves do better.
Romans 8:13 shares that through the spirit man we do mortify the deeds of the fleshly man. This profound knowledge helps me to know that I am not bad or wrong when I suffer through my fleshly attitudes and habits, because my fleshly influence does not go away or die in this life. My reborn spirit man is real and I need to use it like God means for me to. I must always remember that I have a reborn spirit and that I must spend quality time building it up. I must use the spiritual strength that comes from God to quickly get back into my reborn spirit when the flesh directs my thoughts.