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.  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.  Therefore, brethren, we are debtors, not to the flesh, to live after the flesh.  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.  For as many as are led by the Spirit of God, they are the sons of God.  For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father.  The Spirit itself beareth witness with our spirit, that we are the children of God:  And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. - Romans 8:9-17
Let's examine the lesson more closely. Firstly, the word 'flesh' as used by Paul can be highly misleading. He does not mean bodily. Rather, when he speaks of the flesh he means man, both body and soul, in his fallen condition. Hence, he writes in his Epistle to the Galatians that the works of the flesh are "adultery, fornication, uncleanness, lewdness, idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies, envy, murders, drunkenness, [and] revelries" (Galatians 5.19-21 NKJV). Notice, how some of the things listed relate to the body but the ultimate source of all of them is in the will and the mind. Note also how, if we are honest, we are guilty of one or more of these works of the flesh. It should make us shudder then to see what Paul writes next "of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God" (Galatians 5.21). Like the response of the incredulous disciples to a particularly hard saying of Jesus, our question to Paul will likely be "who then can be saved?"
The answer is found, in part, in our epistle lesson. The opening verse reads "ye are not in the flesh, but in the Spirit", that is, you have left behind the fallen state of man and are being renewed by the Holy Spirit. Now, how is this true? The key is to notice how the Spirit is identified in the second part of that opening verse. He--not it--is called the Spirit of Christ. Not the spirit of spirituality or the human spirit, the Spirit of Christ: the Spirit who leads and points to the living Christ. Spirituality that does not point to Christ is not of the Holy Spirit. Leadings of the Spirit that do not lead to Christ, are not of the Holy Spirit. Rather, the Holy Spirit, the Spirit of Christ, makes us to be like Christ. Our union with him and resulting transformation is how Paul can write that we are not in the flesh but in the Spirit.
What does it mean for the Spirit of Christ to make us like Christ? It means first of all that in the flesh—as sinful, fallen humans—we are dead. Christ came in the flesh and by his life of service and obedience, he revealed us to be the sinners that we are, and then, he died for these same sinners. It means that as sinners there is no place for us to stand, either to boast about our good works or even our bad works. I'm sure you've heard 'testimonies' where a person who has had a radical conversion experience gets up only to brag about all the bad things he formerly did. Before that person even had an inkling to sin, Christ died for him. It means that the endless attempts at justifying ourselves, proving ourselves to be right both in relation to others and in relation to God has come to a definitive end. Self-justification is like the punishment of Sisyphus who in Greek mythology is condemned to roll a boulder uphill, only to have it, of course, continually roll downhill. The reality of sin is like that rock, but yet, we go on trying to cloak and justify our sins, figuratively pushing that rock uphill. The one sacrifice for sins that Christ made frees Sisyphus from his endless burden.
What we witness in Jesus Christ is God's unequivocal 'no' to human sin and pride. So, the bad news is that the old Man--the flesh--must and has in fact died. But the Good news is that the New Man--the man renewed by the Spirit--has been firmly established in Christ. In Christ, God has spoken a definitive Yes to man, freely justifying us sinners by his grace, and making a new humanity through the resurrection of Jesus. The Holy Spirit makes us like Christ in his death, yes, but also in his resurrection; verse 10, "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." This New Man has not done anything to justify himself. He has not cooperated with God or advanced in God's service; but rather Christ has firmly established his foundation, and he is the prototype of this new Man. On account of these things Paul can write these bold words earlier in Romans: "we have peace with God through our Lord Jesus Christ" (5:1). We cannot make our peace with God; it has already been done on our behalf in Christ.
So, the Holy Spirit, the Spirit of Christ, makes us like Christ in his death--we die in him--and like Christ in his resurrection--we rise with him to new life and are freed from the guilt and burden of sin, but the Spirit also makes us like Christ in his sonship; verse 14: "For as many as are led by the Spirit of God, they are the sons of God." Sons, not to exclude women or suggest that women be transformed into men, but that we, both men and women, are given the status of the Eternal Son of God, our Lord Jesus Christ.
The true Gospel of the Lord Jesus is so powerful and has implications for every area of human life. If we believe that we freely justified by Christ, then nothing--no person, no thing, no event--is grounds for fear or anxiety. This is the point of the later part of this chapter, but Paul hints at this theme in verse 15: "For ye have not received the spirit of bondage again to fear, but ye have received the Spirit of adoption, whereby we cry, Abba, Father." Abba is the familiar form of address for father in Aramaic. Some scholars have suggested it is equivalent to the term of endearment 'daddy'. The point is clear: we who were alienated from God by our sins, are now children of God, adopted brothers and sisters of our Lord Jesus, a new humanity God is gathering together in Christ. Imagine if rebels against the state, insurrectionists of the most violent type were declared to be forgiven and adopted by the King as heirs along with the King's son. This is precisely our position according to Paul in the final verses of our passage.
What will a Father not do for his children? This is a question to ponder. If it is true that we are God's children, what enemy could damn or curse us with any gravity? We are fed in body and mind from the table of God's abundance even in the presence of our enemies. If it is true, what adversity or trial could we face where we could legitimately fear the permanent loss of any good thing? Our Father shepherds and guides us through all of life's difficulties. If this is true, that we are God's children, who could declare us to be unlovable with any authority? We are wholly loved by Him who is called Love; and his is a love that does not alter or fade, but is steadfast even in the valley of the shadow of death. “For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. The Spirit itself beareth witness with our spirit, that we are the children of God: And if children, then heirs; heirs of God, and joint-heirs with Christ.”