The Biblical concept of ‘sinful flesh’ can be confusing in that it often doesn’t necessarily refer to the physical body alone. The flesh is certainly and nearly always a reference to the body or members of the body in some capacity, but in many Scriptural passages, it is more than that. The sinful flesh is the relationship or interaction between the body and the soul. Apart from God, the body, with its cravings and sensations, makes ruthless demands on our soul. It is what drives our internal desires that lead to sinfulness (Galatians 5:19).
Watchman Nee, who was a Mid-20th century Chinese Christian teacher wrote, “Unlike many philosophers, we [Christians] do not think the flesh is intrinsically evil, but we admit that the body is the sphere where “sin” rules. Therefore, we see in Romans 6:6 that the Holy Spirit calls our body “the body of sin,” because before we experience the dealing of the cross, before we yield our members as weapons of righteousness to God, our body is simply “the body of sin”” (The Spiritual Man, Chapter 10).
Our physical body has certain cravings that are not necessarily bad until those cravings are distorted by sin. The body hungers for food but when unchecked, our need for nourishment can easily lead us to over indulge to the point of gluttony. We have sexual passions, but outside the context of marriage, this is very clearly, and always a sin that causes harm to ourselves and others (Romans 1:26-27; 1 Corinthians 6:18). We are instinctively driven to self-preservation, but when untempered, this can lead us to do terrible things for the sake of gaining the upper hand, such as maiming or murdering our fellow humans.
But as Christians, God’s work of sanctification gives us the power to discipline our bodies and bring those fleshly desires into submission (1 Corinthians 9:27). As entirely sanctified people, if we keep our eyes on Jesus and trust Him fully, then we can maintain complete holiness, not of our own strength but only by the power of His Spirit inside of us.