Doctrine or Ethics?

I'm still working on this page, but I don't think my conclusions will change before I finish. 

(Romans 6:1) What then are we to say? Should we continue in sin in order that grace may abound?
The subject is sin, ethics, behavior, our walk. The question is about "sin." "Sin" is a violation of God's Law. 
1 John 3:4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
Romans 6 is therefore a discussion about ethics. Calvin writes:

     Throughout this chapter the Apostle proves, that they who imagine that gratuitous righteousness is given us by him, apart from newness of life, shamefully rend Christ asunder

Paul's purpose in this chapter is to destroy the idea that we do not have to concern ourselves with obeying God's Commandments on the grounds that Christ's righteousness has now been imputed to us. Calvin continues:

     The Apostle now takes notice of that most common objection against the preaching of divine grace, which is this, -- "That if it be true, that the more bountifully and abundantly will the grace of God aid us, the more completely we are overwhelmed with the mass of sin; then nothing is better for us than to be sunk into the depth of sin, and often to provoke God's wrath with new offenses; for then at length we shall find more abounding grace; than which nothing better can be desired." The refutation of this we shall here after meet with.
(Romans 6:2) By no means! How can we who died to sin go on living in it? We ought not live in sin.
We ought not violate God's Law.
This is the message of Paul. Action, not mere belief.
(Romans 6:3) Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? (6:4) Therefore we have been buried with him by baptism into death, so that, just as Christ was raised from the dead by the glory of the Father, so we too might walk in newness of life. Jesus died and was resurrected. Analogously, we have died to sin so that our ethics might be made new. Calvin writes:

Paul now assumes a second principle: We truly grow up into the Body of Christ only when His death produces its fruit in us. Indeed he teaches us that this fellowship of His death is the focal centre of baptism. It is not a washing alone, but also the mortification and putting to death of the old man, which is there set forth.
(Romans 6:5) For if we have been united with him in a death like his, we will certainly be united with him in a resurrection like his. Paul is not speaking of "our physical death and resurrection," according to John Murry, but " he is dealing with our death to sin and our resurrection to spiritual life." This means ethics, obedience to God's Commandments.
(Romans 6:6) We know that our old self was crucified with him so that the body of sin might be destroyed, and we might no longer be enslaved to sin. (7) For whoever has died is freed from sin. Ethics, not mere belief; that is the subject here.

The purpose of crucifying the old self was so that we might no longer be enslaved to sin.
(Romans 6:8) But if we have died with Christ, we believe that we will also live with him. But crucifying the old self is just half the story. Once dead, the old self must be resurrected into a new self, obedient to God's Commandments.
(Romans 6:9) We know that Christ, being raised from the dead, will never die again; death no longer has dominion over him. Paul continues to hammer on the analogy. Just like Christ, we must move from death to life. Paul is explaining why Christians don't sin ("so that grace may abound").
(Romans 6:10) The death he died, he died to sin, once for all; but the life he lives, he lives to God. Obedient to God's Law: Is there any other way to describe the life that the resurrected Christ lives? Paul is saying this is the kind of life the Christian must live.
(Romans 6:11) So you also must consider yourselves dead to sin and alive to God in Christ Jesus. We must consider ourselves. Some would say we should only consider the imputed righteousness of Christ. We must consider that disregarding God's Commandments is not an option for us. 
(Romans 6:12) Therefore, do not let sin exercise dominion in your mortal bodies, to make you obey their passions. We are not to let sin reign in our lives. We are to be committed to obeying God's Law. We must continually make choices to let God reign in our lives. We must do what God commands.
(Romans 6:13) No longer present your members to sin as instruments of wickedness, but present yourselves to God as those who have been brought from death to life, and present your members to God as instruments of righteousness. Our ethical orientation must change. We can no longer disregard God's Commandments. We must present ourselves before God, with whole-hearted allegiance to His Commandments.
(Romans 6:14) For sin will have no dominion over you, since you are not under law but under grace. What does it mean to be "under law?" There have been many suggestions, but there is no reasonable interpretation of this phrase which contradicts "keeping the law." Paul began this chapter by saying that we must not sin, which the Bible defines as transgressing God's Law.

• sin = not keep God's Commandments.
• not sin = not not keep God's Commandments.
• not sin = not not keep God's Commandments.

So we are not "under law," but we continue to keep God's Commandments. "If you keep My Commandments, you will abide in My love, just as I have kept my Father's Commandments and abide in His love." (John 15:10)
(Romans 6:15) What then? Should we sin because we are not under law but under grace? By no means! Should we sin? No. Should we keep God's Commandments? It's obvious: yes.
(Romans 6:16) Do you not know that if you present yourselves to anyone as obedient slaves, you are slaves of the one whom you obey, either of sin, which leads to death, or of obedience, which leads to righteousness?  
(Romans 6:17) But thanks be to God that you, having once been slaves of sin, have become obedient from the heart to the form of teaching to which you were entrusted,  
(Romans 6:18) and that you, having been set free from sin, have become slaves of righteousness.  
(Romans 6:19) I am speaking in human terms because of your natural limitations. For just as you once presented your members as slaves to impurity and to greater and greater iniquity, so now present your members as slaves to righteousness for sanctification.  
(Romans 6:20) When you were slaves of sin, you were free in regard to righteousness.  
(Romans 6:21) So what advantage did you then get from the things of which you now are ashamed? The end of those things is death.  
(Romans 6:22) But now that you have been freed from sin and enslaved to God, the advantage you get is sanctification. The end is eternal life.  
(Romans 6:23) For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.