[whiteandnerdy]

I think you're setting an unreasonably high bar.

Christianity has a high degree of continuity with Judaism, but rejects important aspects of Jewish theology, such as Kosher and Sabbath-keeping. So while Christianity accepts large amounts of Jewish theology, and extends new ideas, it doesn't universally accept everything that came before it.

Similarly, Islam accepts large amounts of Christian theology (and indeed reintroduces some Jewish practice) and brings new beliefs with it, but doesn't bring every tenet along.

Admittedly Jesus' divinity is a very big part of Christianity to reject; but then, the idea of the trinity would be an equally big pill to swallow for a Jew ("hear, O Israel: the LORD your God is one").

[pulse7]

First Christians were Jews which kept the Sabbath and didn't eat unclean meat (even Jesus kept the Sabbath). Then later Christians changed many practices and diverged from the first teachings. During Reformation attempts were made to come back to original Christianity. Seventh-day Adventists for example keep the Sabbath holy and don't eat unclean meat - just like Jesus did! And there are also some other, smaller denominations which also keep the Sabbath holy - like Seventh-Day Baptists.