Most of it is based on old Hebrew ritual, with only a few parts of the Bible. I'm not a big expert on it, and my Hebrew is very bad. I do attend a pretty orthodox shul when I go because I enjoy the ritual and community. But oftentimes, I don't go at all. And I don't keep kosher.
When I first started attending this shul, I told the rabbi that I really didn't believe in God and was more of an internationalist and Marxist than a believer in religion. Actually, I'm an atheist. But he said that this was okay with him. He said I just should keep some of the mitzvot (commandments). Because of the recent rise of anti-Semitic attacks in this country (USA), I have started wearing my kippah (skullcap). I have kept my head covered when I go outdoors especially for years, much like the one in my avatar.
The Hebrew at my shul is based on the old Ashkenazi pronunciation. It's quite different than Modern Hebrew pronunciation. A lot of words are different. Hebrew stopped being a spoken language long before Christianity came on the scene. Jews back then spoke Aramaic. So nobody really knows how ancient Hebrew was pronounced. Modern Hebrew only started in the middle of the 19th century with the rise of political Zionism (FYI, I'm no big fan of political Zionism). The pronunciation of Modern Hebrew is based on the pronunciation of the Sephardic Jews, who were expelled from Spain during the inquisition, and north African and Arabic Jews. The grammar of modern Hebrew is rather different than ancient Hebrew.
When a large number of Jews from the middle east came to Europe around 1000 years ago, a sizeable number settled in Alsace-Lorraine and parts of what is now southern Germany. They spoke a form of old Middle-High German. However, they used the Hebrew alphabet to write it. Their dialect evolved into a language, based on German but having a lot of Slavic, Lithuanian, and Aramaic words. It became a distinct language and is now rather different than any form of German. It was called "Yiddish-Deitsh" which means "Jewish German." Over several centuries, it was just called "Yiddish," which means "Jewish." Although still written with the Hebrew alphabet, Yiddish is quite different from Hebrew, which is a close cousin to the Arabic language. Something like 70% of native Yiddish speakers died in the holocaust, and what had been a very active Yiddish literary, theater, and artistic scene has never really recovered. Today, most Yiddish speakers live in the United States.
My apologies if I've gone too off topic here. I can provide some answers to questions if people have them, but I won't feel comfortable engaging in flaming or Jew jokes. It's just a little too close to home. I hope you'll understand.
Ancient Hebrew was one of almost idential dialects used in the region of Canaan, i.e. phoenician, hebrew, syriac. Even the alphabet was that of the Phoenician. It was also very close to Akkadian, Nabatean, and Arabic of the peninsula.
Thanks to both of you. A great deal of learned information here. Definitely "The Best Of Three Worlds". (or more)