Paul is clear in Galatians 5 that there is an ongoing battle for the Christian –

“But I say, walk by the Spirit, and you will not gratify the desires of the flesh. For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, for these are opposed to each other, to keep you from doing the things you want to do.”

We have an enemy – sin – and it is constantly opposing us. Our job is to kill it, mortify it. But what if we don’t? Does sin shift into neutral? No. It acts like any other enemy seeking to gain ground.

John Owen explains –

1. Unmortified sin weakens the soul and deprives it of strength. See Psalm 38. Have you ever felt sick in your soul because of unconfessed sin?
2. It untunes and unframes the heart itself and entangles its affections. Have you ever struggled to sincerely tell God that He is your portion? Does your soul have other lovers?
3. It fills your thoughts with things that please the flesh. Do you understand the power and influence of your thought life? Paul said in Romans 12 that we are to be transformed by the renewing of our minds. Your thoughts supply your affections either unto righteousness or unrighteousness.

These are some of the ways sin works and it is always working. But remember this – Christ has already done the decisive work. So we work because he already has.

“We know that our old self was crucified with him in order that the body of sin might be brought to nothing so that we would no longer be enslaved to sin…..Let not sin therefore reign in your mortal body to make you obey its passions.” Romans 6:6,12