The Bible teaches that the Christian's enemy is a threefold one: the flesh, the world and the Devil.
The flesh is the old self life, the fallen nature in each one of us. The world is the world of mankind around us that is alienated from God and opposed to His rulership. The Devil, or Satan, includes also the fallen angels whom he controls.
The basis for our victory over this threefold enemy has already been laid for us in Christ.
With regard to the flesh, we read in Romans 6: "Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. For he that is dead is freed from sin" (vv. 6,7).
With regard to the world, we read in Galatians 6:14: "But God forbid that I should glory, save in the cross of our Lord Jesus Christ, by whom the world is crucified unto me, and I unto the world."
This is why the Lord could tell us in John 16:33, "In the world ye shall have tribulation: but be of good cheer; I have overcome the world."
Further light is thrown on this subject in 1 John 5:4,5: "For whatsoever is born of God overcometh the world: and this is the victory that overcometh the world, even our faith. Who is he that overcometh the world, but he that believeth that Jesus is the Son of God?"
"For I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day" (2 Tim. 1:12).