When is the last time that you were really tempted to sin? Did it feel like gravity was pulling you toward doing something that we wrong? Did it feel like Paul’s words in Romans 7:15-20:
For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate. Now if I do what I do not want, I agree with the law, that it is good. So now it is no longer I who do it, but sin that dwells within me. For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. For I do not do the good I want, but the evil I do not want is what I keep on doing. Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me.
The flesh is our internal enemy and a seed of corruption that lingers in us until our glorification following death. In brief, the flesh is our fallen internal resistance to obey God and our desire to put self-interests above God’s interests.
“Flesh” sometimes means a physical body, as when the “Word became flesh.” But the Bible does not locate our sin in our physicality, as ancient and contemporary Gnostics do. The sinful deeds of the flesh come from every part of our person. Paul uses “flesh” to refer our innate propensity to sin against God; he says that the flesh is the seat of our sinful passions, the realm of sinners, and the source of our evil desires.
The Bible commands Christians to put to death sinful desires. Puritan theologian John Owen called this the “mortification of sin.” Because sin is a deadly enemy, we have to kill it before it kills us. The opposites of mortifying sin include excusing sin, tolerating sin, or merely wounding sin by attempting to manage it rather than kill it. Mortification is Holy Spirit-enabled conviction followed by repentance of sin, faith in God, worship of God, and perseverance in holiness so that sin remains dead and joy remains alive.
Whatever his tactics, Satan’s ultimate goal for believers is typically a compromised and fruitless life beset by heresy, sin, and ultimately death. This demonic opposition is increasingly pronounced for those who serve God most faithfully. As the Puritan William Gurnall said, “Where God is on one side, you may be sure to find the devil on the other.”
As a Christian, the Bible teachers that you are a new person with a new identity in Christ, new power in the Holy Spirit, and new desires in your soul. But, until we rise from death we drag around with us our old flesh that tempts us to go back to our old life rather than forward to our eternal life. This is why Christians desire sinful things.