Through the Mosaic Law, God makes clear His unyielding standard of perfect righteousness. Because we're all fallen, none of us can meet this standard (Romans 3:23); we disobey the precepts of God's written code and commit treason against an infinitely good God, so therefore our crime and deserved punishment are infinite. The purpose of the law is to scream to us, "Sinner, sinner!" and heighten our guilt at our disobedience (Romans 5:20) so that we would be driven to receive Christ who saves us from our sinful inability to obey the law and the condemnation it brings. When we accept Christ as our Lord and Savior, Christ takes our sin and condemnation upon Himself (Romans 8:3) and in return we receive His perfect righteousness from a life of full obedience to the Law, so that the righteous requirement of the Law might be fully, impossibly fulfilled in us sinners (Romans 8:4). Our sin then no longer separates us from God and we are able to enjoy full fellowship with Him.This narrative is (I believe) something very much like the version of the Gospel that is presented in many evangelical Christian circles all over the country and world. So before I start to criticize parts of it, let me make clear why I'm doing so. I'm not merely trying to be a smart aleck by painting my Christian brothers and sisters as fools. I'm not trying to make myself some kind of guru who has all the answers about the Gospel; that would be Jesus, not me. What I am trying to do here is to recognize the need for a constant, divine restlessness in our faith and how we express it.
Between our established "orthodox" doctrine, statements of faith, and monolithic works of theology, there is a great temptation for us to think we have some spiritual truth "figured out", especially when that truth is supposed to be as foundational as the message of how you get Saved, the Gospel. That is, we know "enough" of it to stop questioning it and proclaim and teach it as the Truth that every Christian needs to believe. We stop being restless about our doctrine and instead rest in it, content to leave it where it is, as if any of our finite words could fully capture the gloriously boundless revelation God has given us in His word. So with the Gospel presentation. We have taken a flawed definition of the Gospel, possibly like the one I gave above, and treated it as the Real Thing, thereby blinding ourselves to the hangups it might cause with people. If God's goal for His people really is perfection, then we always need to keep growing.
With that said, you may well be wondering: that's the Gospel; it's great! What could this lunatic possibly find wrong with it? I'd like to get at an assumption it makes by asking a question:
Does the Law primarily exist to produce perfect obedience to a certain set of commands, or to produce a certain kind of people? Or, more colloquially, does the Law primarily consist of do's and don'ts, or is it a blueprint for how God's redeemed people should be and live?
You may be thinking I'm making a false dichotomy; love for God has always been the greatest commandment (Deuteronomy 6:5. Matthew 22:37), and we love God by keeping His commandments (1 John 5:3). So there is no tension between obeying His commands and becoming the kind of people He wants us to be, is there? No, there isn't supposed to be--but that doesn't meant such tension can't exist. Sinful man will make a way! Even if our concern for obeying God is meant to be equivalent to our love for God, that doesn't stop anyone from elevating one over the other
I don't have any kind of reasoned, logical, Biblical argument to "prove" why the Law, as commonly referenced by the New Testament authors, is better thought of in terms of is mission to produce a "people of God" characterized by shalom, God's desire of peace, justice, and flourishing for His creation. Instead, I will simply try to show how it "just makes sense" by pointing out questions that the Law-as-commanded-action narrative raises but does not itself answer (at least to my satisfaction).
Jesus did not obey the letter of the Law. I'm honestly amazed people don't make a bigger deal of this fact. For example, in Matthew 12:1-8, Jesus' disciples, while walking through a grainfield on the Sabbath, pick and eat some of the heads of grain. The Pharisees (who I picture as deploying "minders" to observe Jesus 24/7 for unlawful behavior) point out that Jesus' disciples are breaking the Law--not by stealing grain, but by doing work ("harvesting" grain) on the Sabbath. And they're right! Jesus responds not to explain how their interpretation is wrong and they are really keeping the Sabbath as you might expect, but by giving other examples of legitimate breaks from the ceremonial laws. If the whole point of righteousness is to obey the Law, then this makes no sense and Jesus is just making excuses. The Pharisees knew the Law backwards and forwards; Jesus does not question their knowledge of the Law but appeals to a higher priority than obedience to the letter: "I tell you, something greater than the temple is here."
Jesus and the apostles redefine or even change the ethical demands of the Law. For example, in Acts 10, Peter has a dream in which God presents him with a variety of animals (some of them "unclean" according to the Law) and tells him to "kill and eat". Let me make this unmistakably clear: God is telling Peter, a Jew, to disobey a commandment He previously gave the Jews (in Leviticus 11). His justification for this is not some exception or loophole that allows Peter to eat without breaking the commandment; God merely says, "What the Lord has made clean, do not call common." And yet Jesus said, ""Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished." (Matthew 5:17-18) If by "the Law" you mean (as the Pharisees did) the specific ethical imperatives given to the Jews that must be obeyed at all costs, this promise of Jesus is repeatedly shown to be false by passages like this. But if the ultimate purpose of the Law is not to get people to act and live in certain, divinely dictated ways but to transform them, then it's easy to see how Jesus fulfilled the Law instead of doing away with it.
Or consider the contrast between the seventh commandment, "You shall not commit adultery", and Jesus's teaching on adultery in Matthew 5:27-30. Using the commandment as a springboard, Jesus explains that it doesn't just mean the physical act of adultery--lusting after a woman is committing adultery with her in your heart. Wait, wait, wait! What kind of careful, historical-grammatical reading of Exodus 20 did Jesus use to draw that conclusion? Where was it in the original text? Well, Jesus is God, so He has the authority to add to previously given commands. But even so, wouldn't it at least have been nice to know for the Israelites and not given as a "Surprise!" thousands of years later? But again, if the point of the Law is not simply rote obedience but the creation of a people of shalom, then Jesus' teaching on adultery makes perfect sense. It doesn't even constitute a change to the commandment, only a clarification. I don't think there is supposed to be any distinction between the state of our heart and our acts of obedience to God. The Pharisees had made this distinction and become masters of it, so Jesus tried to remove it by showing the two to be synonymous.
The end goal: what does fulfilling the Law mean? In the narrative I gave at the start of this post, Jesus' fulfillment of the Law basically amounts to checking all the boxes it lays out because we couldn't be obedient enough to check them ourselves. This impossibly blank list of checkboxes is supposed to be the "legal demand" of the Law (Colossians 2:14): you need to check all the boxes by obeying each rule to be righteous, or Jesus needs to do it for you with His life of perfect righteousness substituted for your own. The problem with checking boxes is that it doesn't change you. If your goal is simply to "do" the requirements of the Law, understood as rules to be obeyed, you might be able to do it, but you'll be the same person as you were before but with a full checklist. Actually, you'll be a worse person--you'll be a Pharisee.
Let's stop this double-mindedness whereby we view the Law as this impossible heavy set of moral burdens that Jesus took on Himself because we couldn't carry them, as if something instituted by God could be reduced to an obstacle to salvation to be overcome. (Also, paradoxically, by God) What if the "righteous requirement" of the Law is understood to be not a requirement to do certain things, but to become a certain kind of person--a person remade in the image of Christ? What if the intent of the Law was always to produce and govern a society made up of this kind of people, and this purpose can finally, exclusively be fulfilled via Christ's life, death, and resurrection transforming us? The proof of this, for me, is not that I simply see that it is true but that by this understanding I can see more clearly the beauty and purpose of the Gospel of God.