To answer your good question, let’s read Romans 8:9-10, “But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his. And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness.” 

The standing before God for every believer is that we are “not in the flesh, but in the Spirit.” (Verse 9).  If one truly believes in the Lord Jesus Christ, he receives the Holy Spirit and thus can be described as being “in the Spirit.”  We certainly still have the flesh and sometimes we might walk according to it, but our standing is sure…we are NOT in flesh, but we are in Spirit. 

Romans 8:1 presents us with this glorious truth, “Therefore there is now no condemnation at all for those who are in Christ Jesus. (NASB).  We learn here that we are “in Christ Jesus” where verse 9 teaches us that we are “in the Spirit.”  In addition to that, 1 John 4:15 teaches us that “Whosoever shall confess that Jesus is the Son of God, God dwelleth in him, and he in God..”

Not only are we “in the Spirit”, “in Christ Jesus”, and “in God”, verse 10 of our chapter tells us that

Christ is in us!  (Verse 9 says the Spirit dwells in us.  1 John 4:15 says God dwells in us!)  Because Christ is in the believer, the body is dead because of sin.  Since our body of sin is dead before God, we should reckon it as dead and evidence that by not giving into the wants, lusts, and desires of the body.  If we allow the body its own will, it will produce NOTHING BUT SIN.  The way for the believer to get power over the sin that is in him is to regard the body as dead.  But, to those who are in Christ, the Spirit is life because of (or, by reason of) righteousness. 

Now, with that in mind, let us consider Romans 8:11, “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 your mortal bodies by his Spirit that dwelleth in you.”

For the believer in Christ, “the Spirit of him that raised up Jesus from the dead” does indeed dwell in him.  Ephesians 1:13 makes that very clear, “In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, YE WERE SEALED WITH THAT HOLY SPIRIT OF PROMISE.” To quote William Kelly on Romans 8:11, “This is a rich and precious word.  As sure as you now have the Spirit of God dwelling in you – the Spirit that raised up the humbled man Jesus, He that raised up the glorious One, who was made Lord and Christ, will raise up your mortal bodies.” 

It is good to notice how Romans 8:11 speaks of the resurrection of Jesus (the humbled One…Philippians 2:5-11), and the resurrection of Christ (the glorified One…Titus 2:13).  It is as Jesus that he humbled Himself and as Christ that He is the glorious One. 

What a sure hope for the believer in Christ!  Having our mortal bodies quickened (made alive) by the Spirit of God that indwells each believer will be the final act in our redemption…when our bodies are glorified and made to be just like our Savior’s body.  Romans 8:23 tells us, “And not only they, but ourselves also, which have the firstfruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, to wit, THE REDEMPTION OF OUR BODY.”  1 John 3:2 gives us great assurance, “Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, WE SHALL BE LIKE HIM; FOR WE SHALL SEE HIM AS HE IS.”  (CC)  (509.4)