Romans 8:9-11 meaning

Paul tells the Roman Christians you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you (v 9). As believers, we have a new identity and new ability to obey God. Paul reiterates to his readers (Roman Christians) that they are no longer slaves to their sinful bodies, but now live with the Spirit of God as their ever-present Helper. 

But if anyone does not have the Spirit of Christ, he does not belong to Him (v 9). God sent the Spirit as a Helper. All Christians have the Holy Spirit with and in them, acting as a leader, if the Christian is willing to follow Him (1 Corinthians 3:16; 1 John 4:13). 

Paul states this assurance in the negative: "If you don't have the Spirit of Jesus then you are not a believer in Jesus." This is one of the amazing realities of believing in Jesus: He actually sends His Spirit to dwell in us. And there are no exceptions. We do not have to earn this supernatural power. We simply have to learn how to use it. In this sense, believers are like superheroes who must learn to use and harness their superpower for good.

In verses 10 and 11, Paul contrasts the resurrection power of life brought by the Holy Spirit with the flesh, which brings death. This connects back to Romans 7:24, where Paul asks "Wretched man that I am! Who will set me free from the body of this death?" He maintains that he still lives in a body of flesh, which leads him to experience death by leading him to obey the law of sin. Paul answers his own question by declaring that Jesus is the one who frees us from the body of death, the flesh.

The struggle between flesh and spirit is evident throughout the book of Romans, and Paul wants to make clear that Christ's death was sufficient to bring righteousness to us in the presence of God, that Grace has abounded more than sin ever could. But for us to experience that in our daily life, we have to face two concurrent realities of having a dead body of sin that wants to control us, while also having the living spirit of Christ dwelling in us because of our faith in Him: If Christ is in you, though the body is dead because of sin, yet the spirit is alive because of righteousness (v 10).

For the believer, it is through the Holy Spirit that life is given. The Spirit of Him who raised Jesus from the dead dwells in you (v 11). Eventually, this life-giving will be made totally complete; just as Christ was raised from the dead, we also can look forward to being fully resurrected when we leave this earth (1 Corinthians 15:51-53): He who raised Christ Jesus from the dead will also give life to your mortal bodies through His Spirit who dwells in you (v 11). But in the present, we still have this mortal body with this old self, this old sinful nature in it (Romans 6:6), and also with the Spirit of Christ in it.

One of the salvations, or deliverances, that we have to look forward to is the time when we're saved from having to walk around with our sin nature. Our new resurrected body will not have a sin nature. That is our hope of glory in many respects. But that is something that's in the future. 

Paul refers to this later on in the letter to the Romans. He also expresses this sentiment elsewhere in his writings, such as in 2 Corinthians 5:4 where he refers to his body as an "earthly tent": "For indeed while we are in this tent, we groan, being burdened, because we do not want to be unclothed but to be clothed, so that what is mortal will be swallowed up by life." 

In the following passage, Paul writes that God made us for this purpose, and that the Holy Spirit is a promise for this eventual Glorification Salvation, this deliverance from our current sinful body.

So, God gives life to the mortal body even though we have this weak sinfulness remaining in us. We can live, not as a slave to sin and death, but as a resurrected person. How? Through the Spirit.