For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh.Galatians 5:17
In every believer's heart there is a constant struggle between the old nature and the new. The old nature is very active and loses no opportunity of employing all the weapons in its deadly arsenal against newborn grace; while on the other hand, the new nature is always on the lookout to resist and destroy its enemy. Grace within us will employ prayer and faith and hope and love to cast out the evil; it takes to itself "the whole armor of God"1 and wrestles vigorously. These two opposing natures will never stop struggling as long as we are in this world.
Bunyan's Christian fought Apollyon in a battle lasting three hours, but the battle of Christian with himself lasted all the way from the entry Gate to the River Jordan. The enemy is so securely entrenched within us that he can never be driven out while we are in this body: But although we are closely followed, and often in fierce conflict, we have an Almighty helper, Jesus, the Captain of our salvation, who is always with us and who assures us that we shall eventually be more than conquerors through Him. With such assistance the newborn nature is more than a match for its enemies.
Are you fighting with the adversary today? Are Satan, the world, and the flesh all against you? Do not be discouraged nor dismayed. Fight on! For God Himself is with you. Jehovah Nissi is your banner, and Jehovah Rophi is the healer of your wounds. Do not fear, you will overcome, for who can defeat Omnipotence? Fight on, "looking to Jesus";2 and although the conflict is long and tough, the victory will be sweet, and the promised reward will be glorious.
From strength to strength go on;
Wrestle, and fight, and pray,
Tread all the powers of darkness down,
And win the well-fought day.
1) Ephesians 6:11
2) Hebrews 12:2