1 What shall we say then? Shall we continue in sin, that grace may abound?
2 God forbid. We who died to sin, how shall we any longer live therein?
3 Or are ye ignorant that all we who were baptized into Christ Jesus were baptized into his death?
4 We were buried therefore with him through baptism unto death: that like as Christ was raised from the dead through the glory of the Father, so we also might walk in newness of life.
5 For if we have become united with him in the likeness of his death, we shall be also in the likeness of his resurrection; [ASV]
6 knowing this, that our old man was crucified with him, that the body of sin might be done away, that so we should no longer be in bondage to sin
7 for he that hath died is justified from sin.
When speaking of our having "died to sin" and having been "baptized into his death" - this is to be understood, as John Stott writes in his Romans commentary, in a 'legal sense'. It is self-evident that we did not literally die when Christ was crucified on the cross. Rather, in that God "chose us in him before the foundation of the world" [Eph. 1:4], our life and destiny, by God's gracious will, are irrevocably connected to Christ our Head. We have been made party to God's covenant of promise, i.e. salvation in Christ, by God's choosing; a covenant that Christ alone fulfills. And he, as our representative head, accomplished this through the death he died to sin once for all who are in him (Rom. 5:15-18). So then it follows that the ultimate death penalty for sin no longer has a claim on us. We are set free from the reign of sin and death by Jesus' propitiatory sacrifice on the cross.
Therefore in real time, through baptism and faith, we were united with Christ in the "likeness of his death"; a penalty bearing death that is effectual for us according to God's promise. So that through Jesus' death on our behalf the "body of sin" (the evidence of our guilt before the Law) has been put away. It cannot touch us in that the evidence and guilt of our sin was imputed to Christ and borne by him on the cross (2Cor. 5:21a). God's justice is completely served and satisfied. Paul speaks of this having been accomplished through baptism, and this is true inasmuch as water baptism is truly an effectual sign and seal of the inward Holy Spirit-powered grace of God through faith in Christ Jesus.
United to Christ through faith, Jesus is our means or ark (for safe passage through seas of death, 1Pet. 3:20-21) of dying to sin and death, having been buried with him. Death could not hold him, for in his own person he fully met all the just requirements of God's holy law. Having died for the sins of his people, he was raised by the Spirit in keeping with the justice of God (Rom. 2:13b). And also we who are united with him have risen with him out of death into newness of life. And we have the down payment of that resurrection having been given the blessing of regeneration, a new heart and "right-will" inclined to righteousness and love (Rom. 5:5; 6:17-18). Jesus Christ rose from the dead fully justified by his law-keeping and by faith in him alone we, for whom he died, are now "justified from sin", declared as righteous before God through Christ's merit only (2Cor. 5:21b; Rom. 4:5).
This is the ground floor upon which we rest, walk, and stand as Christians. As Edward Mote, 1797-1874, wrote "All other ground is sinking sand." So, in a manner of speaking, we look backward to what Jesus accomplished for us helpless sinners through his death and resurrection in order that we may move forward, living for him as we are led by his Spirit. Any other ground of merit and service before God will see us devolve into the subtle yet deceitful box canyon of attempting to establish a false merit through our works in order to attain some measure self-justification. For we yet remain helpless inasmuch as being able to truly do anything that is free from the stain of sin. And we should not deceive ourselves into taking refuge in our good works, our "spiritual" experiences, our epiphanies, or our godly intentions, even as the Holy Spirit faithfully leads us into those good works "which God prepared beforehand that we should walk in them." [Eph. 2:10]