There are three unholy agents that is against every Christian.
That is the world, the flesh and the devil. I believe your flesh is the worse of the three. The reason is that it is simply attached to you and it is always so near.
Three UNHOLY Agents Against the Christian
1 John 2:15-17 (KJV) Love not the world, neither the things that are in the world. If any man love the world, the love of the Father is not in him. 16 For all that is in the world, the lust of the flesh, and the lust of the eyes, and the pride of life,