Originally An Answer on Quora: To the Christian Whom Is Considering Mainstream (Non-Messianic) Judaism

 If you’re a Christian, you already practice what was recognized as a form of Judaism by even the Pharisees (albe begrudgingly) until 90 CE/AD at Yavne—whether you are regrafted into the olive tree (a Jew whom believes in Jesus) or grafted into the olive tree (a gentile whom believes in Jesus). You could therefore denominationally practice Messianic Judaism (The ethnic distinction of “Messianic Jewish” belongs to Ethnically-Jewish Christians—whether Patrilineal, Matrilineal, or mixed-blooded Jews—alone.).

If you’re thinking about converting to mainstream (Non-Messianic) Rabbinic, Karaite, or Samaritan Judaism, you should consider that you would more than likely be asked to deny (not just remain faithless to Jesus; also outright deny) Jesus by the rabbi or ḥakham whom would oversee your conversion. Keep in mind that if you deny Christ, He will deny you. If you want to take that risk, though, that’s up to you—just remember that you are risking what the Scriptures warn about denying Christ and therefore trampling the Son of God underfoot. As the Scriptures say, “If we deny Christ, He will deny us. If we are faithless, He will remain faithful, for He cannot deny himself.”