God says the Sabbath is a seal between him and HIS people.
4th Commandment, KEEP (protect, guard) the Sabbath.
That's a start........what does that have to do with judaism?
Depends what you mean by Judaism TBH...
Often when I use it, I refer to being an Israelite (or a converted gentile) who follows the Torah, as in the actual Torah as opposed to the Talmud or any other external teachings (which some people try to refer to as "torah" too).
Usually when you mention "Judaism" though, the majority of people understand the meaning to be Orthodox Judaism, that I wear a kippah and probably have long sideburn curls etc, when that's not what I mean at all.
Really though, Judaism is more of a blanket term, because it's accurate to say that Jesus/Yeshua taught Judaism, but he didn't teach what the Pharisees taught then and the rabbis teach today. It's also accurate to say that the rabbis today teach Judaism, and they generally totally reject Yeshua/Jesus and what he taught. Dark chocolate and white chocolate are all referred to as chocolate, but generally if you speak of chocolate, the listener will think of milk chocolate until you specify otherwise, that's more or less what happens with the word Judaism too.
Keeping the Sabbath is definitely a part of Judaism, it's one of the most important parts of the Torah that sets the people apart who love both the God of Israel AND their fellow man, and the people who just love their fellow man (as many un-believing gentiles definitely do, or at least try to do) alongside refraining from bowing to other gods (literally bowing to or praising statues and false gods, and handing over sovereign authority over you to other men that govern). This doesn't, however, mean that it's something that you have to belong to any specific sect of Judaism to join in, whether born Jewish (Israelite) or whether born gentile and you choose to follow the instructions in the Torah and follow them, including the sabbath, you can be said to be "Jewish" in faith and action, under the blanket term.
Do the Sabbath keeping Baptist appear Jewish? How about the Church of God which also keep the feasts? Gentiles don't do it like the Jews. But they are as obedient as they congregation leads them to be. Some individuals within the group always do more. You find a lot of these individual Gentiles within Messianic Judaism keeping Torah better than the Jews.
I agree - there are a lot of minor details within the Talmud that even bring the orthodox Jews to directly violate Torah. Let me give you an example, Leviticus 11 makes it completely clear that we are NOT to eat, or even touch the carcass of a pig (or any other unclean animal), and also of the clean animals, that we're only supposed to eat their flesh, not their fat, bones, blood etc.
In modern day Orthodox Judaism, it is taught that a Jew may eat foods containing pig gelatine, skin and bone, because it has been processed. They say that that since it has been processed to the point at which it no longer resembles being part of a pig, and has been made safe during the processing. Many foods and medicines containing these substances are certified Kosher, although they contain substances directly derived from the carcass of pigs, and while on a technicality, I can see their point that they're arguing, it is totally in violation if you take the Torah at face value, since it doesn't ever say "unless you heat it at 80 degrees and spin it around in a churn full of chemicals when you learn how to do so", it just says don't do it.