1Jn_2:23 Whosoever denieth the Son, the same hath not the Father:
You left off the most important part of 1 John 2:23:
"Whoever denies the Son does not have the Father either; he who acknowledges the Son has the Father also."
3.As did Maimonides and Yehudah Halevi,[1] we acknowledge that Christianity is neither an accident nor an error, but the willed divine outcome and gift to the nations. In separating Judaism and Christianity, G-d willed a separation between partners with significant theological differences, not a separation between enemies. Rabbi Jacob Emden wrote that “Jesus brought a double goodness to the world. On the one hand he strengthened the Torah of Moses majestically… and not one of our Sages spoke out more emphatically concerning the immutability of the Torah. On the other hand he removed idols from the nations and obligated them in the seven commandments of Noah so that they would not behave like animals of the field, and instilled them firmly with moral traits…
http://cjcuc.com/site/2015/12/03/orthodox-rabbinic-statement-on-christianity/
Whereas the Gospel of John was written to unbelievers, this epistle was written to those who were already believers (5:13).[9] It seems likely that its audience was largely gentile rather than Jewish, since it contains few Old Testament quotations or distinctly Jewish forms of expression.[2] The epistle was probably carried by itinerant missionaries to different churches throughout the region and read aloud to the congregations.[10]
Uh, no. "Acknowledge," homologeo, to assent, confess, profess. The immediate context is that Jesus is the Christ, which everyone who denies, in the preceding verse, is described as an "anti-Christ."
A Jewish unbeliever who rejects that Christ is the Messiah is damned, and without Christ they have nothing.
It seems likely that its audience was largely gentile rather than Jewish
Which is entirely irrelevant, since the verse is true for all, regardless if they are Jews or Gentiles. Both Jews and Gentiles are regarded as guilty under the law, and thus cannot be saved except through Christ.
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