I can’t promise that you’ll like my handling of this. Our difficulty is not merely that Western Christianity reads the words wrong, but that Western Christianity has a totally different set of assumptions about reality from what Paul held when he wrote this.
Let’s start with Jesus. You can review His teaching, but He didn’t have a problem with the Law of Moses. You need to read “Law” as “Covenant” and think about how it was an imperfect statement of God’s divine moral character. Jesus noted that the Covenant was imperfect, yet still binding. In the minds of ancient Hebrew people — at least among those educated enough to think about it — a covenant was the commitment between two persons. It’s not at all like a Western contract, which demands the performance of people, but isn’t particular about the actual humans, only the performance. Covenant is very personal and very particular between two individuals. It’s a commitment, a matter of trust and faith.
Yet it also binds those who inherit the requirements of the covenant. It was binding on the family, clan, tribe, etc., based on the role and authority of those who swore to the covenant. This is why the Fall affects all humans, because everyone on earth is descendant from Adam and Eve. It was a matter of transgressing the covenant between God and His Creation, in which Adam and Eve were the executors of God’s will in some portion of Creation (the Garden). Their descendants inherited that covenant and all the penalties for Adam and Eve’s failure. Thus, we are all born under the Curse of the Fall, because we still have the covenant duty to keep the Garden.
Paul struggles to explain this to people who grew up under Roman culture. The Romans had a different approach to things. Not quite what Westerners have now, but Rome and the West are closer to each other than either is to Hebrew thinking. At the same time, there are Jewish Christians in his audience who have a Greco-Roman understanding of Moses, which is very similar to the Talmud. We must never forget that Jesus said the Talmud was not Moses. Thus, Judaism is not faithful to the Covenant of Moses, but a perversion of it. Paul tends to address things from the viewpoint of countering Talmudic perversion.
So Paul starts with Jesus as the ultimate fulfillment of Moses, in the sense that the ritual requirements were satisfied in Christ’s sacrifice. Furthermore, His sacrifice was sufficient to cover all humanity, Gentiles included. That means that Jesus fulfills the Covenant of Noah, as well. Instead of talking about the Fall, Paul points out the effects of the Fall, making us by default in rebellion against the Garden covenant with God. We are “sinners” in that sense, and Jesus’ death on the Cross paid the penalty on our behalf.
Then he launches into a bunch of symbolic arguments that confuse Western readers. In the process, he is striving to answer the false arguments made by Talmudic minds. He is not answering the questions likely to occur in our modern Western minds. It’s not that we can’t get what he’s saying, but we have to approach it from the Talmudic point of view. If there’s an Apostle who understands that viewpoint, it’s Paul with his equivalent of a PhD in synagogue studies, with all the peculiar concepts and structures of debate.
It’s not that there was no “Law” of God prior to Moses, but that revelation had never been so plainly revealed in a covenant setting as it was with Moses. Yes, the Covenant of Noah was in force between Adam and Moses, but how likely was your average human to know much about that? They would know only if they had felt drawn to seek revealed truth. And then they would have to wade through a bunch of lore and ancient tales that may or may not contain the real truth from God. But with Moses, there were no questions, since it was all written out and backed by the most impossible miracles, including the Exodus itself.
But then Paul forges ahead into the symbolism of Adam and Christ. What it boils down to is this: If we inherit the broken covenant with God via Adam as our blood-kin progenitor, we can can also inherit the redemption in Christ as our adoptive kinsman. And in the process, the term “Law” becomes associated with the written record of the Covenant of Moses, while “grace” becomes a code word for the Covenant of Christ.
And “sin” becomes a reference to the dominion of Satan. Once again, Satan is God’s jailer/slaver, a high ranking noble servant of God rather like Potiphar was with Pharaoh. If you break the covenant with your ruling feudal lord and family head of household, you could be remanded to the custody of this jailer who made you work for him as a slave. Thus, you can continue serving “sin” (the nickname for Satan and his dominion over sinners) or you can accept the pardon Christ offers and be free to serve Him.
The pardon comes tied to the requirement for death of self. Never once in any New Testament teaching does this require any kind of “perfection” was we think of the word. Instead of emphasizing the soldier at war imagery, it’s more like the image of a slave under the jailer’s dominion who dies in their chains and escapes to another realm of existence. They are permitted to join themselves to the death of Christ, to participate in His death on the Cross, and escape the enslavement that way. It’s all symbolism and perfectly valid in God’s eyes.
Thus, Paul warns that the old slave self will struggle within us to come back to life. But insofar as the slave lives, it’s a living death in chains. Paul encourages us to stay away from those chains. “Don’t let sin reign in your mortal body!”
How were people “saved” under Moses? They had to take the Law very seriously. Instead of viewing it as a burdensome thing, they had to understand that their best interest was bound up in faithfulness to the Covenant. You had to invest yourself in that Covenant and personify it as the character and personality of your God. Somewhere along that path, we know that some folks were touched by the Spirit of God and changed. There were clearly people under Moses who lived in God’s favor. But under Christ, you could be granted the same touch of God’s Spirit before you spent years pursuing the Law.
That is, our sinful nature can be broken as a gift, not as a result of long effort. That’s where this business of “you are not under Law, but under grace” comes from. You don’t have to struggle against your sin nature; it’s broken right now. But don’t be lazy about it. You aren’t free to ignore the Law, only free from that long hard path. You are permitted to see through the Law to the personal nature of your God before you start working on obedience. But the whole point is to enable obedience. It’s not an excuse to be as self-willed and libertine as a slave. Keep living it up like that all you do is restore the chains.
And then you die the same miserable death as the slaves of sin. That’s the fruit of sin. The fruit of willful obedience is holiness and all the unspeakable riches of faithfulness to God.