For as many as are led by the Spirit of God, these are sons of God.  (15) For you did not receive the spirit of bondage again to fear, but you received the Spirit of adoption by whom we cry out, “Abba,  Father”.  (16) The Spirit Himself bears witness with our spirit that we are children of God, (17) and, if children, then heirs – heirs of God and joint heirs with Christ, if indeed, we suffer with Him, that we may also be glorified together. 

The letter to the Romans was written by the apostle Paul. Paul has been addressing the perpetual contest of the corrupted nature of man with  the new life of the faithful.  He now turns to the consolation of this battle  which is that the faithful are exempt from the power of death, in Christ, provided they live in the Spirit. At the moment of faith in Christ, men and women are pardoned and forgiven for sin and transformed/regenerated  by the now indwelling Spirit of God.

Being in the flesh means devoting oneself to the world and those who do so proceed to death and cannot partake of the peace of Christ. Men by themselves are calable of nothing but ruin as there is no life in our corrupted nature. Man cannot earn salvation, it is only of the Lord. The free gift of grace and gratitutous remission of sin can never be separated from the Spirit of regeneration and the children of God are counted spiritual because of the newness of life in them.  We are justified in Christ – made right with God – but there is no justification without the Spirit –  doing the bidding of the Spirit is also necessary for sanctification.  Only those ruled by the Spirit of God are indeed sons of God and their evident godly behavior is how God marks His people.

Paul tells his readers that they did not in Christ receive the spirit of bondage – by this he means the Old Testament Jews received the Law of Moses which commanded and forbade.  The Law made man aware of sin and restrained man by fear.  But with the coming of Christ and the clear light of the gospel the faithful receive the Spirit of adoption whereby God forgives us our sin and deals with us as a Father.  Under the guidance of the indwelling Spirit there is genuine assurance of being right with God, in Christ, and an elevated state of mind which man on his/her own could never achieve

Our verses today end with the caveat that the faithful will be co-heirs with Christ Jesus who came to glory by the cross, if we suffer with Him.  This is the order of salvation, not the cause and shows us how God governs His people