(This is written from a "Christian" perspective. By "Christian" I mean a follower of Christ, not Catholic or Protestant or any sub-group. Just a believer of the Holy Bible.)
As mentioned by others, whether or not Yeshua (Christ) is the Messiah, is the focal point around which most of the differences between Christianity and Judaism revolve.
Because followers of Judaism do not believe the Messiah has arrived yet, they believe they are still under the old Laws (aka the old Covenant). The Laws which were written in the Old Testament include the dietary restrictions (Kosher diet) and the laws regarding Temple sacrifices, among many, many others.
Judaism (like Christianity) does have some divided "denominations" based upon differences of opinion regarding Scriptures and such.
For instance, some Jews believe that the Jewish people should not move back to Israel because in the Old Testament, Yahweh (God) exiled the Jewish people from Israel... and they believe that they are still forbidden to leave their exile. (see [Link](Mouse over link to see full location) for more info)
Followers of Yeshua (Christ) believe that the entire Bible includes both the Old and the New Testament. The New Testament states that if anyone breaks even one of the Laws, they are guilty of breaking all of the Laws. And since everyone has broken at least one of the Laws, none of us is righteous, none is worthy, we have all sinned. Since the wages of sin is death, that means none is worthy of eternal life.
So, to summarize, many of us believe that the purpose of the Law is to show us how imperfect we are, and how we fall short of Yahweh's goals for us.
Followers of Yeshua believe that is why He came to earth, to live the perfect life that none of us could. So we believe He obeyed every single one of Yahweh's Laws, perfectly. (remember, Yeshua was Jewish so he would have lived the Jewish lifestyle under the Jewish Laws.)
We believe that when Yeshua sacrificed himself for us, He was paying our debt (the wages of sin is death, so he died for us) and because He is the sinless, spotless Son of Yahweh, His death is enough to pay for all of our sins, if we accept His Gift.
Because of this we believe we are under a New Covenant... We have been given grace. "...for ye are not under the law, but under grace." Romans 6:14
As for the Sabbath, it's true that most Christians celebrate the Sabbath on Sunday. While the Biblical (and Jewish) Sabbath is actually from sundown Friday to sundown Saturday. There are many different opinions on why this happened... But here is a bit of info on the most widely accepted reason:
"The Catechismus Romanus was commanded by the Council of Trent and published by the Vatican Press, by order of Pope Pius V, in 1566. This catechism for priests says: "It pleased the church of God, that the religious celebration of the Sabbath day should be transferred to 'the Lord's day. Sunday.'"
But many followers of Yeshua don't believe that there was any reason to move the Sabbath, so they observe the original Sabbath.
For instance, we (myself and my husband) now observe the original Sabbath from sundown Friday to sundown Saturday, and we are not "7th Day Adventists" (another division of Christians who observe the original Sabbath day).
On a personal note, I must say that since we have started observing the original Sabbath, we have felt it to be more restful and peaceful. :-)
By the same token, some Christians also think that eating Kosher (or close to it) is a good idea. Not because it's a law we have to obey, but because Yahweh knows better than us...
This one is my personal theory, but I don't think Yahweh would exclude a food just to be arbitrary. I mean, pork tastes very good (to me, anyway), and I don't think Yahweh would tell his children not to eat something tasty, just because He felt like it. I think He has a very good reason and I think it's because it's bad for us. He didn't want His children eating things that would hurt their health.
Part of the kosher dietary requirements eliminates being able to eat scavengers. Pigs are scavengers that will eat poop, dead things, and just about anything else. Catfish are scavengers too (and because they don't have scales, they aren't kosher), and crustaceans (like crabs and lobsters), and mollusks (like clams and oysters) are bottom-feeding scavengers too, and not kosher. It seems reasonable that it could be bad for our health to eat things that live by consuming questionable things.
So even though I am what people consider to be a Christian, I gave up eating pork and other scavenger creatures, not because I think it's a sin, but because I believe that Yahweh has our best interests at heart.
There is also a difference between Jewish people and Judaism. A Jewish person is, racially, someone who is a descendant of Jacob (son of Isaac, who was the son of Abraham) from the Old Testament. Jacob was also called "Israel", thus his descendants are also called Children of Israel or Israelites. He was the father of twelve sons, who represent the twelve tribes of Israel.
Descendants of Jacob do not necessarily practice Judaism. Just because someone is born of a certain heritage, doesn't mean they will automatically practice the traditional religion of their fore-fathers. So there are Jews who do not practice Judaism.
And from what I understand, non-Jews can convert to Judaism... Though I'm not sure how that works.
There are also Jews who DO believe that Yeshua is the Messiah, and thus have those Christian beliefs. Some call themselves Messianic Jews. Usually, they still observe the Sabbath from sundown Friday to sundown Saturday, among other Jewish traditions. Though there are some Jewish believers that follow the more traditional Christian paths, and consider themselves to be Jewish Christians, Hebrew Christians, or Christian Jews: [Link](Mouse over link to see full location)
TheOldOne answered Tuesday May 9 2006, 12:27 pm: That's a major difference - perhaps THE major difference - but there are many other differences, too. For example, Jews practice circumcision as a religious ritual, and Christians don't. You may find it interesting to know that for Muslims circumcision is also a religious ritual, by the way.
Jews keep kosher, Christians don't.
Other differences include confession (for Catholics), the ritual of transubstantiation, most religious holidays, the Sabbath - for Jews Saturday is the day of rest, for most Christian sects it's Sunday - and I could go on and on. Christianity is derived from Judaism, but the relationship is complicated and generally not close.
The Torah of Judaism is basically the Old Testament of the Christian Bible. Jews do not recognize the New Testament, of course.
It's also important to note that there are many different sects of Christianity, and several different types of Judaism, too! These are all different from each other in different ways.
Wikipedia is a good place to start learning. Start with these links for more information:
JNS answered Tuesday May 9 2006, 3:44 am: That is the main difference. The whole old testament is used and taught in both judism and christianity and the new testament which includes Jesus is only used in christianity. However Jews and Christians pray and believe in the same God. [ JNS's advice column | Ask JNS A Question ]
Igotamonopoly answered Tuesday May 9 2006, 3:36 am: There are other minor differences. Might I suggest google?
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