Being jewish is determined by birth lineage, or conversion. Normally the bloodline is passed down on the mother's side.
My Dad was Jewish, my Mom wasn't.
Whether or not messianic jews get their inspiration in Christ, know that they are either jewish or not depending on their lineage, and not by what they believe.
Understanding that, know that the case against them, which I was studying today, is based scripturally on an apostate book, which I believe, though am not certain of, is the Unitarian Bible. That version of the story is rooted in secular humanism. Many of the quotations that non messianic jews believe are attributable to Christ are not actually found at all in the canonical gospels.
Now, I am not anti semitic. What I think that non messianic jews might find out is that there is going to be some guy who shows up that will deceive them into believing that he is Mosiach. He will be known by his works.
That's all I have to say on that subject. I cannot tell Jews what to believe. I am a gentile and a christian. Who am I to tell them about God?