David Stern is the translator of the Comple Jewish Bible. He is a Mesianic Jew, and his Bible is very popular among Messianic Jewish believers, because it restores a Jewish entity to the Gospels. He also wrote a book called "The Jewish New Testament Commentary" In this book he attempts to explain the Hebrew Idioms behind the Greek writings, from a Jewish perspective. Here are some 'excerpts' from this book:
Rev 2:9 I know your works, and the affliction, and the poverty; but you are rich. And I know the evil speaking of those saying themselves to be Jews, and they are not, but are a synagogue of Satan.
Rev 3:9 Behold, I give out of the synagogue of Satan those saying themselves to be Jews, and they are not, but they lie. Behold, I will make them come and bow down before your feet, and they shall know that I loved you.
" Yochanan (John) writes about Gentiles who call themselves Jews but aren't - on the contrary, they are a synagogue of satan, the adversary, Perhaps they, like the gentile Judaizers of the book of Galatians, adopted a smattering of Jewish practices and tried to force them on Gentile believers. They may have subjected themselves to a legalistic perversion of the Torah. They apparently organized a pseudo Messianic synagogue. Their false doctrine probably led them to wrong and immoral behavior, since false doctrine usually does. They probably drew Gentile Christians away from the truth, and thereby threatened the Messianic community. Virtually all commentators ignore the obvious and straightforward interpretation that Yochanan (John) is talking here about Gentiles who pretend to be Jews."
"Should it nevertheless be thought improbable that Gentiles would call themselves Jews, Hebrews or Israelites, consider the following modern examples. The 'British Israelites' regard the British as the Ten Lost Tribes. The Mormons not only consider themselves to be the Ten Lost Tribes but regard themselves as Jews and everyone else (real Jews included) as Gentiles. A sect of mostly American-born blacks consider themselves the true Hebrews; several thousand of them are living in Israel. All of these are outside the pale of Christianity. In addition, scattered about are well-meaning Gentile Christians whose strong identification with and love for the Jewish people has made them believe,without a shred of evidence,that they are actually Jewish themselves.In fact, some years ago a congregation was expelled from the American Lutheran Church because, along with a general drift into weirdness, its pastor and dozens of its members claimed to have heard from God that they were really Jews; many even said they knew which tribe they belonged to."
"Without exception this phenomenon of Gentiles imagining and asserting they are Jewish when they are not leads to strange patterns of doctrine and practice. Such people are not accepted by Jews as Jewish; nor, as this verse shows, are they to be accepted by Christians as Christian. Isolated and self-defensive, they can easily become prideful, neither obeying the Torah nor showing brotherly love to Yeshua's (Jesus) real followers. It is easy to see why Yeshua (Jesus) does not regard them as harmlessly neutral but pegs them as the synagogue of the adversary."
(All above writings in "quotes" from the Jewish New Testament Commentary, by David Stern)