In older translations of the Bible this is generally called `the flesh’, in more modern versions ‘the sinful nature’. It does not refer to our physical bodies, but to our old, pre-Christian self that continues to haunt us and drag us down. This is the `enemy within’, and can be the most difficult to deal with. But if we don’t fight it, it will destroy us. The Israelites were warned, long before they entered the Promised Land, that they were not to live as the Canaanites did – otherwise they would lose their homeland, as the Canaanites did (Leviticus 18:24-28).
When we become Christians, our sins are forgiven and we receive the Holy Spirit to transform us into children of God. The problem is that we carry on sinning! Despite our new desire to please God, and despite the help of the Spirit, we cannot totally overcome the tendency to sin that is part of our old nature. Its persistence is what makes us so vulnerable to the influence of the world and the attacks of the devil. This is why the Bible teaches that sin is inevitable even for Christians (I John 1:8,9).
However, we must not be satisfied with this state of affairs. God continues to forgive us when we sin, but His grace does not give us a licence to sin (Romans 6). Rather, now that we belong to God, we must stop surrendering to our old sinful nature. This isn’t simply a matter of willpower, because our will is not strong enough to overcome our flesh. It is fundamentally a matter of attitude, and of trust.
We have to begin by recognising that our old nature is still there. Without this self-knowledge, we cannot hope to make any progress. Then we must `crucify’ the old nature, or `put it to death’ (Colossians 3:5; Galatians 5:24). Crucifixion was a slow and lingering death, and we must not expect our sinful nature to die quickly and easily. In fact, killing it can be a frustratingly slow and painful process. “Whoever wants to be My disciple must deny themselves and take up their cross daily and follow Me.” (Luke 9:23) Our old nature has been tied down, rendered powerless, and given a mortal wound; but it is not finished yet. Having nailed it to a cross, we must now leave it there, shutting our ears to its screams for mercy; like a real executioner, we must show it no pity.
We are not on our own in this struggle; the Holy Spirit will help us. He is the agent of change in our lives – working with us, motivating us, providing us with energy, desires and resources that do not come naturally to us, and persevering with us until we become like Christ. But He will not act without our co-operation. We can’t just sit back and let Him do all the work; we have to keep making a conscious choice to live by the Spirit and march to His tune.
Imagine a man who keeps two dogs in a cave – two dogs who are continually fighting each other. This is like the continual conflict between the Holy Spirit (living in us) and our old nature (Galatians 5:17). The man can choose which dog he feeds. The dog that is well fed will grow stronger and will gain the upper hand over the animal that is starved. So if we indulge our sinful nature and pander to its desires, moral decay will set in and sin will eventually take over our lives. But our other option is to ‘please the Spirit’ by feeding our minds on God’s Word, sharing fellowship with other Christians, and resisting the pull of the sinful nature (Galatians 6:7,8). Every act of obedience will strengthen our relationship with God and increase our harvest of the Spirit’s fruit. This is the path to holiness; there are no short-cuts.