Are Gentiles obligated to obey the Mosaic law, as Armstrongites and other Sabbatarians have argued?
Yes and no. It depends on what you mean by law!
1. Let's look first at the "yes" side. In his writings to Gentile churches, Paul often cites the Old Testament law as an authority for moral conduct. Here are some examples:
Romans 3:20: "For 'no human being will be justified in his sight' by deeds prescribed by the law, for through the law comes the knowledge of sin" (NRSV).
Romans 8:3b-4: "[God] condemned sin in the flesh, so that the just requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit."
Romans 13:8-10: "Owe no one anything, except to love one another; for the one who loves another has fulfilled the law. The commandments, 'You shall not commit adultery; You shall not murder; You shall not steal; You shall not covet'; and any other commandment, are summed up in this word, 'Love your neighbor as yourself.' Love does no wrong to a neighbor; therefore, love is the fulfilling of the law."
I Corinthians 9:7-11: "Who at any time pays the expenses for doing military service? Who plants a vineyard and does not eat any of its fruit? Or who tends a flock and does not get any of its milk? Do I say this on human authority? Does not the law also say the same? For it is written in the law of Moses, 'You shall not muzzle an ox while it is treading out the grain.' Is it for oxen that God is concerned? Or does he not speak entirely for our sake? It was indeed written for our sake, for whoever plows should plow in hope and whoever threshes should thresh in hope of a share in the crop. If we have sown spiritual good among you, is it too much if we reap your material benefits?"
I Corinthians 14:34: "[W]omen should be silent in the churches. For they are not permitted to speak, but should be subordinate, as the law also says."
Galatians 5:14: "For the whole law is summed up in a single commandment, 'You shall love your neighbor as yourself.'"
Ephesians 6:1-3 (which is technically Deutero-Paul, for liberal scholars): "Children, obey your parents in the Lord, for this is right. 'Honor your father and mother'-- this is the first commandment with a promise: 'so that it may be well with you and you may live long on the earth.'"
You can see that Gentiles are under the authority of the Mosaic law, for Paul quotes it as an authority on how they should live.
This runs counter to two popular anti-law views within Protestantism. The first one states that Christ has abolished the Mosaic Torah while replacing it with a new law, the law of Christ. This is the position of the Church of Christ.
Granted, the New Testament contains a number of new laws and commands (Matthew 5-7; John 13:34; I Corinthians 9:21; Galatians 6:2), and it often exhorts believers to behave in light of Christ, without rooting its morality in the Old Testament law (Philippians 2:2-12; Ephesians 4:12; Colossians 3:13). Consequently, Sabbatarian Des Ford is wrong to deny that the New Testament is a book of legislation, for it does appear to present a new Torah for God's people.
But we have seen that Paul also appeals to the legislation of the Old Testament. In I Corinthians 9:9, he even goes so far as to call his source "the law of Moses." You can't get any clearer than that! Essentially, the law of Moses is still authoritative, but it has been supplemented with the teachings and moral example of Christ.
Another anti-law view is that God gave the Torah specifically to Israel, meaning that it's not relevant to non-Israelites. But if we're going to take that approach, then we might as well dismiss all of the Bible's authority. I can easily say, "Paul was writing to the first century church, so it doesn't apply to James Pate." We have seen that Paul treats the Torah as authoritative for Gentiles. Therefore, the argument that "God just gave those laws to Israel" doesn't really cut the mustard, in my humble opinion. Granted, God revealed his perfect will specifically to Israel, but God's standards apply to everyone, Jew and Gentile alike. And, while Paul acknowledges that the Gentiles know enough about right and wrong to be judged apart from the law (Romans 2:14-16), he is clear that the Jews alone possess the oracles of God, which enable them to know God's will and determine what is best (Romans 2:18; 3:2). Sure, the Gentiles can be moral. But the Jews are the ones with access to the "best."
2. On the "no" side, Paul says that believers "are slaves not under the old written code but in the new life of the Spirit" (Romans 7:6). He denies repeatedly that believers are "under the law." Armstrongites maintain that "under the law" means under the law's penalty, but that doesn't work entirely. Paul says in Galatians 4:4 that Jesus was born under the law, and Jesus was not under the law's penalty, for he was sinless. In Galatians 4:21, Paul addresses those who desire to be under the law. Why would anyone want to be under the law's penalty? And Paul states in I Corinthians 9:20, "To those under the law I became as one under the law (though I myself am not under the law) so that I might win those under the law." How can Paul pretend to be under the penalty of the Torah? That makes no sense!
"Under the law" means "subject to the regulations of the Torah." As far as Paul is concerned, that's a life of slavery (Romans 7:6; Galatians 4:21-31). At the same time, being "under the law" can entail being under the law's penalty, since people do not obey it! As Paul says in Galatians 3:10, "For all who rely on the works of the law are under a curse; for it is written, 'Cursed is everyone who does not observe and obey all the things written in the book of the law.'" That's why Paul calls the Old Covenant system a ministry of condemnation (II Corinthians 3:9). Placing oneself under the legal system of the Old Testament is a dead end, in Paul's mind.
Another indicator that Gentiles don't have to obey the Mosaic Torah is Acts 15. A group of Jewish Christians wants to require the Gentile believers to be circumcised and obey the law of Moses. Sabbatarian Ron Dart has argued that the issue here is not the necessity of keeping the law, but rather whether or not people needed to observe it for salvation (see here). For Dart, one cannot earn God's forgiveness through obedience to the Torah, but one should still fulfill the law because it's God's righteous standard.
But Acts 15 doesn't seem to be about why one should observe the Torah (for justification vs. out of obedience). Rather, it appears to exempt the Gentile believers from the Torah's commands. As James says in Acts 15:28-29: "[I]t has seemed good to the Holy Spirit and to us to impose on you no further burden than these essentials: that you abstain from what has been sacrificed to idols and from blood and from what is strangled and from fornication. If you keep yourselves from these, you will do well." The issue at the Jerusalem conference is what Gentiles had to do, not the proper motivation for keeping the law.
Another point: Armstrongites may claim that people are not saved through obedience to the law, but that's not always how they acted! I've heard of ministers who said that people won't enter God's kingdom if they missed the Feast of Tabernacles or worked on the Sabbath. "Oh, but you don't do these things to earn God's forgiveness--you do them to obey God," they may assert. It's still a yoke of bondage, regardless of what justification one attaches to it! I can't believe that Acts 15 is saying, "You Gentiles can't earn salvation through doing the law, but you still must place yourself under its yoke, since that's what your Christian walk is all about." Such a view makes the Jerusalem conference a debate over semantics!
3. So does the New Testament teach that Gentiles have to do the Torah? It depends on how one defines "Torah." If it means that the Gentiles have to observe the ceremonies of the Old Testament in a literal sense, then the answer is "no." But if it entails that they're under the authority of the law, in the sense that they obey its moral precepts and spiritually interpret its ceremonies as shadows of Christ, then the answer is "yes."
Some may think that my explanation is slippery, in that I'm freely defining the "law of Moses" as I see fit in two different contexts. But there are times when one has to do this. Take a look at the following passages on circumcision:
I Corinthians 7:19: "Circumcision is nothing, and uncircumcision is nothing; but obeying the commandments of God is everything."
Colossians 2:11-13: "In him also you were circumcised with a spiritual circumcision, by putting off the body of the flesh in the circumcision of Christ;
when you were buried with him in baptism, you were also raised with him through faith in the power of God, who raised him from the dead. And when you were dead in trespasses and the uncircumcision of your flesh, God made you alive together with him, when he forgave us all our trespasses[.]"
So is circumcision essential or non-essential? It depends on what you mean by "circumcision." In I Corinthians 7:19, Paul is discussing physical circumcision, and he deems that to be non-essential for pleasing God. In Colossians 2:11-13, however, the author talks about the spiritual circumcision of the flesh (which connotes the sinful nature). That is a circumcision that believers need to have!
So do Gentiles have to obey the law? It depends on one's definition of the law!