Notice the verses that lead up to the above verse:

And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness. (Romans 8:10)

If Christ is dwelling in us our body is dead because of the sin that dwells in it but our new born-again inward nature is alive because of the righteousness of the Law that has been imputed to it.

But if the Spirit of him that raised up Jesus from the dead dwell in you, he that raised up Christ from the dead shall also quicken [make alive] your mortal bodies by his Spirit that dwelleth in you. (Romans 8:11)

If the resurrection Life of God is dwelling in us the day will come when that Life will make alive even our physical body. This will take place in the Day of the Lord provided we do not in the present hour destroy our spiritual life by living in the lusts and desires of the first man.

Therefore, brethren, we are debtors, not to the flesh, to live after the flesh. (Romans 8:12)

Because there is no eternal life in our dead body, and because there now is life in our born-again inward nature, we are not obligated to live according to the fleshly soul and mind. We owe the first personality nothing. The duty of the first personality is to be willing to hang on the cross with Christ until the new man is raised to live with Christ at the right hand of God in Heaven.

Now notice:

For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live. (Romans 8:13)

If you live in the desires and thinking of your first personality you will put to death the resurrection life that is in you. When the trumpet sounds there will be no life in you to carry you up to the Lord in the clouds.

However, if you are willing, that is, if your first personality is willing, to put to death the deeds of your body (which is to crucify your first personality), the Holy Spirit will guide and strengthen you so you will gain the upper hand over the sin that dwells in your flesh.

The sin is always forgiven when we confess it and turn away from it. On some occasions the very presence of sin leaves our personality. On other occasions the sin is rendered powerless but we have to maintain the upper hand over it. Maintaining an upper hand over the lusts of our flesh and soul teaches us how to war in the Spirit and serves a useful purpose.

In the Day of Redemption, all remaining sin will be removed from us and we shall be clothed with eternal life. This is true if we have faithfully put to death the deeds of our body as the Spirit points them out to us.

So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation. (Hebrews 9:28)

The believer makes a clear, unqualified decision to henceforth live in the resurrection life of the Lord Jesus, as the Spirit of God enables. To live in the resurrection life of the Lord is a choice we make. It is an attitude, one might say.

To be continued.