The Bible represents Satan as the master manipulator of human nature. Our weakness combined with the devil's influence has led the whole world into sin (Revelation 12:9). Paul explains that "the god of this age has blinded the minds of unbelievers, so that they cannot see the light of the gospel ..." (2 Corinthians 4:4).
Paul reminds Christ's faithful disciples that "you once walked according to the course of this world, according to the prince of the power of the air, the spirit who now works in the sons of disobedience, among whom also we all once conducted ourselves in the lusts of our flesh, fulfilling the desires of the flesh and of the mind, and were by nature children of wrath, just as the others" (Ephesians 2:2-3).
Because of Satan's deceptions and the sinful tendencies of human nature, "all have sinned and fall short of the glory of God" (Romans 3:23). We must understand, however, that the devil cannot force us to sin. He simply influences us through our fleshly weaknesses. But several major areas of our fleshly nature are easily manipulated by Satan.
First, our selfish, fleshly desires often get us into trouble: "Now the works of the flesh are obvious: fornication, impurity, licentiousness, idolatry, sorcery, enmities, strife, jealousy, anger, quarrels, dissensions, factions, envy, drunkenness, carousing, and things like these. I am warning you, as I warned you before: those who do such things will not inherit the kingdom of God" (Galatians 5:19-21, NRSV).
Paul graphically describes the effect fleshly desires have on human behavior. "Therefore God gave them over in the sinful desires of their hearts to sexual impurity for the degrading of their bodies with one another ...
"Even their women exchanged natural relations for unnatural ones. In the same way the men also abandoned natural relations with women and were inflamed with lust for one another. Men committed indecent acts with other men, and received in themselves the due penalty for their perversion.
"Furthermore, since they did not think it worthwhile to retain the knowledge of God, he gave them over to a depraved mind, to do what ought not to be done. They have become filled with every kind of wickedness, evil, greed and depravity.
"They are full of envy, murder, strife, deceit and malice. They are gossips, slanderers, God-haters, insolent, arrogant and boastful; they invent ways of doing evil; they disobey their parents; they are senseless, faithless, heartless, ruthless. Although they know God's righteous decree that those who do such things deserve death, they not only continue to do these very things but also approve of those who practice them" (Romans 1:24-32, NIV).
Second, our natural deviousness, including self-deception, is a major weakness of the fleshly mind. "The heart is devious above all else; it is perverse—who can understand it? I the LORD test the mind and search the heart, to give to all according to their ways, according to the fruit of their doings" (Jeremiah 17:9-10, NRSV).
We naturally look for ways to justify our lusts, our sinful desires, and the behaviors that arise from them. We deceive ourselves into believing that, since our desires are natural, they are not so bad after all. But God's Word reminds us that "there is a way that seems right to a man, but its end is the way of death (Proverbs 14:12; 16:25). Death is the end result of living that wrong way (Romans 6:23).
Third, we have a natural tendency to resent having our fleshly desires limited by rules, even God's rules. Paul explains: "For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit set their minds on the things of the Spirit. To set the mind on the flesh is death, but to set the mind on the Spirit is life and peace. For this reason the mind that is set on the flesh is hostile to God; it does not submit to God's law—indeed it cannot, and those who are in [that is, dominated by] the flesh cannot please God" (Romans 8:5-8, NRSV).
These and other fleshly weaknesses are what we call human nature. Satan takes advantage of our weak and greedy nature by persuading us to rely even more on our emotions, needs and wants than we normally would. But we play our part. Without the positive influence of God's Spirit, we are simply not naturally inclined to live according to God's instructions.
Therefore, Paul warns: "... If you live according to the flesh you will die; but if by the Spirit you put to death the deeds of the body, you will live. For as many as are led by the Spirit of God, these are sons of God" (Romans 8:13-14).