How do Messianic Jews justify the merging of the law-based traditions of the Old Testament and the grace-based message of Christ when Paul specifically warned against doing so in his letter to the Galatians? When we add any kind of dogma or man-made tradition to the Gospel, we're saying that Christ's sacrifice wasn't enough.
To be fair, I don't think any sound, sane or authoratative leader who is an actual Messianic Jew tries to pit Paul's message of grace against the Old Testament. In fact, the movement seeks to put Paul back into his own frame of reference- a pharisaic teacher. I realize of course that the word "pharisee" is not used kindly in many places in the Gospels, but not all pharisees were wrong (eg. Nicodemus) and we should count Paul among those who got it right.
The issue is that no actual sound Messianic Jew (and there only a couple on this forum) sees any contradiction between the OT and the NT.
What might be of interest to you is that looking at Paul through Jewish eyes makes a lot more sense of him, and it in no way diminishes either grace or the proper use of the Law. It does, in fact, spur the reader into a greater desire to serve rather than just understand. It puts the lifestyle of the Christian into the focus that has gone missing because of the recent theological trend for cheap grace.
Secondly, it might be interesting to note that many Christians have forgotten that the best of the teachers in the history of the Church always sought after a better understanding of Paul and the New Testament message of grace through Jewish "Old Testament" eyes. Check out the better old teachers lke Gill, Wesley, Arndt, Spener, Fletcher etc.
Importantly, the Jewish religion- then and now- has never taught that a person is saved by their works, keeping traditions or observance of the Law. However, faith and works are not seen as opposite forces, but two parts of the same object. This is the same in Christianity (hence Paul teaches that Abraham was justified by faith before Sinai ever came into effect) This demonstrates that a proper understanding of the NT is a Judaic understanding, and that the NT is truly a Jewish book.
Judaism then and now also teaches that while all mankind is not under the Torah of Sinai, it is under the moral obligations (given as laws by God) of all human beings. Thus every son and daughter of Noah is under what the church calls the moral law. Again, this validates the NT as Jewish, and elevates moral truth above all
temporal acts of service and worship.
Likewise, the Jewish religion- then and now- has never taught that the whole of the Torah given at Sinai is for everyone to observe. This gels nicely also with the message of the NT. This proves that the Apostles - under the influence of the Holy Spirit- kept to a Jewish understanding of the Torah when they didn't force circumcision and Sabbaths on to the Gentiles. This distinction is in fact very Jewish.
The thing is that today many Jewish Christians like myself fully accept that one's identity is in Christ, and that His body the church is one and all that other NT stuff, but we come from a culture that is rather strong and often closed to the rest of the world. We see that the Church has Christianities that are very inculturated- the Greek Orthodox, The Russian Othodox (all the national autocephalous churches fit in here), the Latin Churches, Americanized Evangelicalism and so forth. So, if they have expressions of Christianity bourne from their cultures- why can't we? I mean, weren't we the among first kind of churches before we got booted out by Chrysostom and others like him?
What I'm getting at is this- no person approaching the NT from a Jewish pov would ever pit grace vs. outward observance of the Sinai Covenant laws. We say many of them have a place today in Jewish life, and we should be free to live the way we always have, but with the understanding that the covenant and law of Christ is the fulfilled Torah.
I do not think that Gentiles should be circumcised, nor do I invite them to lay tefillin with me. I am the senior minister of a Sunday church, but I don't do any work on Saturday either. I attend all the Jewish holidays, but I don't expect Gentiles to come and frankly I don't even invite them. I eat kosher only. I am saved by grace through faith just as my forefathers were before the cross. The NT teaches that I am allowed to live this way, and you are allowed to live your own way, and we should be happy to do that and still care for each other (Rom 14) I rather like that.
However, if someone comes to you and says that you need to keep all the Jewish festivals, the Sabbaths or any other thing like that just tell them that a Jew told you that ain't Jewish, and that's not the right way to read the NT. The Jewish way of understanding is the correct way...and there's a lot of people out there finding new ways to steal the Jewish identity from us and dilute our people into oblivion- which is exactly what forcing everyone into the Sinai law results in.
From what I've read, Messianic Judaism was devised by a group of Evangelical Christians sometime in the 60's as a way of appealing to the Jewish community, who were (understandably) wary of Christianity because of the less-than-stellar way the Church had treated Jews over the centuries. You won't be accepting Jesus--you'll be accepting Yashua. You won't be going to church--you'll be going to a Messianic synagogue. By doing so, they watered down the Gospel, which is something I wouldn't want to be held accountable for on Judgment Day.
God forbid that we should water down the Gospel. But, this is danger in any tradition, Jewish or Gentile. All of us should keep watch for this.