Perhaps I can persuade gentile Christians by asking the following questions: Do we or do we not observe the 10 Commandments? Do we try to do what Jesus would do (WWJD)? Do we believe there is such a thing as sin?
Answer yes to any of the previous 3 questions, and you've committed yourself to upholding the Law. :-)
For example, the 10 Commandments are part of the Law; one might call them a summary of God's commandments in the Law.
And on living like Jesus, Jesus kept God's commandments. We draw this conclusion given this evidence: his telling others to keep God's commandments (Matt 5, Mark 1:40-45), Paul's stating that the commandments define sin; with Scripture's assertion that Jesus never sinned, it implies Jesus followed God's commandments perfectly. Also, Jesus' own actions: he celebrated the Biblical holidays (Passover, Unleavened Bread, and others) defined in the Law, told others to keep the Law (Matt 5), and finally, we have no evidence of Jesus ever breaking a commandment. WWJD? I'll answer that question: for starters, he'd follow God's commandments.
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. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished. Anyone who breaks one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven. For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven.
-Jesus, in his fundamentals of the faith sermon in Matthew's gospel
Sometimes we tend to ignore Scripture like the above because it doesn't fit our modern, Western doctrines. We instead favor of some of Paul's statements about the Law, causing the confusion we have on the law today.
The next piece is sin: if you believe in sin (that is, right and wrong in God's eyes), then one must also believe in the Law, which defines sin.
The purpose of the Law
One attractive piece of the Law for Christianity is its clear guidelines for right and wrong. The New Testament isn't a book of laws, but rather, a book about Messiah; so without a clear guideline for right and wrong, we're left with confusion. And confusion has abounded: look at some modern "progressive" Christian churches, such as the United Church of Christ, where sexual immorality including homosexuality among church pastors is both tolerated and accepted. Without the Law, how do we know homosexuality is wrong?
The Law has a perfectly legitimate function. Without its clear guidelines for right and wrong, moral behavior would be mostly guesswork. Apart from the succinct, surgical command, "You shall not covet," I could have dressed covetousness up to look like a virtue and ruined my life with it.
-Paul, in his letter to Rome
Paul's right on about the coveting commandment, but the same could be said for the other 612 commandments in the Law, everything from lying to cheating to stealing to sexual immorality to murder. It's all laid out in God's commandments in the Law, and without it, we have no guide, no absolute mappings, of what's right and wrong.
But just having the Law sitting there does no good; we try to follow God's commandments, but even then we still sin; we're a sinful lot and enjoy doing evil things. Paul comments on this:
I've spent a long time in sin's prison. What I don't understand about myself is that I decide one way, but then I act another, doing the very things I absolutely despise. So if I can't be trusted to figure out what is best for myself and then do it, it becomes obvious that God's commands, the Law, is necessary.
But I need something more! For if I know the Law but still can't keep it, and if the power of sin within me keeps sabotaging my best intentions, I obviously need help! I realize that I don't have what it takes. I can will it, but I can't do it. I decide to do good, but I don't really do it; I decide not to do bad, but then I do it anyway. My decisions, such as they are, don't result in actions. Something has gone wrong deep within me and gets the better of me every time.
It happens so regularly that it's predictable. The moment I decide to do good, sin is there to trip me up. I truly delight in the Law, but it's pretty obvious that not all of me joins in that delight. Parts of me covertly rebel, and just when I least expect it, they take charge.
I've tried everything and nothing helps. I'm at the end of my rope. Is there no one who can do anything for me? Isn't that the real question?
The answer, thank God, is that Jesus the Messiah can and does. He acted to set things right in this life of contradictions where I want to serve God with all my heart and mind, but am pulled by the influence of sin to do something totally different.
-Paul, in his letter to Rome
This is a key few understand: the Law is necessary to tell us what sin is, however, it does not save us from sin. Paul says of the Law and it's saving power:
Messiah redeemed us from that old sinful life by absorbing the Law completely into himself. Do you remember the Scripture that says, "Cursed is everyone who hangs on a tree"? That is what happened when Jesus was nailed to the cross: He became a curse, and at the same time dissolved the curse of death that breaking the Law brings. The Law alone never made anyone righteous; you must have faith before you're set straight with God. Anything less is nothing but rule-following.
-Paul, in his letter to Galatia
He's right, if you don't believe in God but follow the Law, you're still nothing. It isn't a slam on the Law so much as it is a glorification of faith in God. Faith is so important, that without it, all our good behavior amounts to nothing. James confirms this:
If you really keep the Law found in Scripture, "Love your neighbor as yourself," you are doing right. But if you show favoritism, you sin and are convicted by the law as lawbreakers. For whoever keeps the whole law and yet stumbles at just one point is guilty of breaking all of it. For he who said, "Do not commit adultery," also said, "Do not murder." If you do not commit adultery but do commit murder, you have become a lawbreaker.
Do you want evidence that faith without works is useless? Was not our ancestor Abraham considered righteous for what he did when he offered his son Isaac on the altar? You see that his faith and his actions were working together, and his faith was made complete by what he did. And the scripture was fulfilled that says, "Abraham believed God, and it was credited to him as righteousness," and he was called God's friend. You see that a person is justified by what he does and not by faith alone.
As the body without the spirit is dead, so faith without works is dead.
-James, in his letter to the 12 tribes of Israel dispersed through the world
An interesting correlation! If we don't have faith, following the commandments is useless (one might say certain modern Judaic Jews fall under this grouping). However, if we have faith but don't have works, our faith is useless (I contend that some modern Christians fall under this grouping). What works is James speaking of? The only "works" defined in Scripture, of course: the Law -- he says it it right there in the text.
You're already following the Law, more or less
Most Christians follow the Law without explicitly knowing it, at least to some degree. We don't murder, for example, and we don't curse, lie, and so on. At least, that's what we preach, and we try to live like this. Wouldn't you know it, all those things we refrain from are sins, defined in the Law. Paul comments on this interesting development of Law-following gentiles without them ever having known the Law:
If you sin without knowing what you're doing, God takes that into account. But if you sin knowing full well what you're doing, that's a different story entirely. Merely hearing the Law is a waste of your time if you don't actually do it. Doing, not hearing, is what makes the difference with God.
When gentiles like you who have never heard of the Law follow it more or less by instinct, you confirm its truth by your obedience. This shows that the Law is not something alien, imposed on us from without, but woven into the very fabric of our creation. There is something deep within us that echoes God's yes and no, right and wrong. Our response to God's yes and no will become public knowledge on the day God makes his final decision about every man and woman. The message from God that I proclaim through Jesus the Messiah takes into account all these differences.
-Paul, in his letter to Rome
Interesting, eh? So if you're already following the Law, more or less, then what am I babbling on about? Well, I am addressing the false doctrine that the Law has been abolished. I hope by now you agree that it is not abolished and has a very real purpose for today. Also, gentile believers in Messiah are fine with the Law until it requires them to make a lifestyle change. For example, the commandments about not murdering, not lying, not cheating: we're all hunky-dory with those. But those commandments that would require of us to change our diet, or stop working for the Lord's day of rest, well, we kind of fudge it and cherry pick what we want to define as right and wrong. That in itself is not right, and is what I'm addressing in this post.
Paul mentions above how we shouldn't sin (break the Law). Does a Christian man murder? Does a believer in God commit adultery? Every man sins, so yes, even Christians do these things. The difference for us is that we know those things do not please God, so we do our best to refrain from those things. We try to do good works and try to live a Godly life. But how do we know what's Godly? How do we know what's good? How do we even know murder, stealing, lying, cheating is wrong? The author of 1 John tells us all these things:
If we claim to be without sin, we deceive ourselves and we're liars. If we admit that we have sinned and turn from those things, God is faithful and just and will forgive us our sins and purify us from all unrighteousness. If we claim we have not sinned, we make him out to be a liar and his word and his commands mean nothing.
My dear children, I write this to keep you from sin. But if anybody does sin, we have one who speaks to the Father in our defense—Jesus the Messiah, the Righteous One. He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.
We know that we have come to know him if we obey his commandments. The man who says, "I know him," but does not do what God commands is a liar, and the truth is not in him. But if anyone obeys the commandments in his word, God's love is truly made complete in him. This is how we know we are in him: Whoever claims to live in him must walk as Jesus did.
What does God command? Did Jesus preach some commands different that God's commands?
There is only one set of commandments, my brothers in Messiah. Messiah taught something not foreign or new, and he didn't come to start a new religion. What a terrible shame our modern doctrines have placed this dark, negative connotation on God's commandments.
One of their religion scholars spoke for them, posing a question they hoped would show him up: "Teacher, which command in the Law is the most important?"
Jesus said, "'Love the Lord your God with all your passion and prayer and intelligence.' This is the most important, the first on any list. But there is a second to set alongside it: 'Love others as well as you love yourself.' These two commands are pegs; everything in the Law and the Prophets hangs from them."
-Jesus, in Matthew's gospel
If the Law can be summed up as loving God and loving others, what's the problem, my friends? A common denominator of those 2 commands is love. Surely, if the sum total of the commandments is love, why are we even debating the Law?
If the commandments are kept, keep them out of love for God. Knowing full well the Law cannot make us righteous on its own merits, keep the commandments because we love God and love his ways. Likewise, we know that without obeying God's commandments, our faith is worthless. Make your faith worth something by living what you preach.