I want to do a brief deep dive into my frequent assertion that Messianic "Jews" are, in fact, Christians and that Christians cannot be Jews. Every time this comes up a bunch of people - mostly Messianic "Jews" and appropriative Christians - show up to argue with me.
They assert that if a Jew converts to Christianity, they remain a Jew and therefore Jewish Christians are a thing. And *technically* this is true - "once a Jew, always a Jew" is a thing. *Technically* it would be more accurate to say that "Jewish Christians" are apostates.
But while it's more *technically* accurate, it's more misleading. Because unless you know that apostasy is a complicated thing in Judaism, and that there are different classes of apostate, and what the legal restrictions and status are for them, it creates a false impression.
Converts from Judaism to Christianity are meshumadim, as distinct from apikoros and koferim. There's ambiguity in the status of meshumadim going back at least as far as 100 CE, but there is a general consensus that they are treated as non-Jews in all aspects *except* familial.
What that means practically is that *except* for matters of marriage and parenthood, a meshumad is treated as a gentile. They cannot pray with Jews. They aren't mourned as Jews when they die. They aren't counted in a minyan, and they cannot receive Torah honors.