Romans 5

I was interested to note that according to Anders Nygren (Commentary on Romans), Romans 5 is seen as an aside, a parenthesis, by many commentators.
That doesn't make sense to me. Romans 1:18-3:20 portrays humanity as under God's wrath, under the power of sin, condemned by the law, and not helped by it but rather driven further into sin by it, and doomed to die. Romans 3:21-5:11 explains what God has done outside of me, portraying the righteousness that is from God and is appropriated by faith.
Something has been done for me, that assures me of eternal hope, God's love and final salvation from wrath. But one more step needs to be made in the argument, or Romans 6ff won't make sense. I need to be shown that I am not just saved from things happening to me by something happening for me, but that something has happened to me: I have come under something new. I am not under wrath, sin, law and death, but under Christ and righteousness. Justification is not simply a legal deal outside of me, but it impacts on my relationship with everything that I was under, because I have been shifted out of the old humanity and into the new one. Neither the symbolism of baptism and its impact on my sinning (Romans 6:1-14) nor the tyranny of the law and its ending (Romans 7:1-6) makes any sense without understanding my transfer explained in Romans 5. Does it?
I'm beginning to think Romans 5:12-21 is the key to Romans, even if Romans 8 is the high point and Romans 9 the point at which the monergism of the book is driven home.
Anyway, I prayed very differently this morning, praying that I would live the life of one baptised into Christ and free from law's tyranny, as appropriate to one under Christ and not in Adam, and as I did so, it was so obvious sin just doesn't fit with who I am by grace in Christ.