The part of Hebrew scripture which is considered most sacred, as it is the only part considered to have been directly handed to Moses by God, is the 5 books of Moses, called "Torah" (meaning "Law") which represents the first part of the Hebrew Canon of 24 books (Tanakh).
(For Muslims, the equivalent would be the Koran, which is seen to have been dictated to Mohammad by God - Allah, whereas all subsequent works, such as Hadith and Tafsir, are not considered as divine or as sacred)
These 5 books of Moses contain all 613 commandments by which the Jewish people are commanded by God to live their lives as a collective body. No one person is capable of fulfilling all 613 commandments, as some relate only to men, others only to women, some only to priests (Kohanim), others for example, only to farmers.
These 5 books, together called the "Torah" (Pentateuch in Greek) are considered as the basic and Divine code of "Written Law" for Jews and all Israelite/Jewish Sects.
The Torah is considered the most sacred or holy of the body in the complete Hebrew canon (Tanakh).
The 613 written commandments in Torah, which represent a code of religious, moral, spiritual and political life for each individual Jew, governing behaviour, responsibilities and obligations from birth to death, are called in Aramaic "Mitzvot De'Oraita"(Written commandments).
The books which follow Devarim (Deuteronomy), beginning with the book of Yehoshua (Joshua - KJV), are attributed to Nevi'im (Prophets) and Ketuvim (Chronicles - KJV) and are not considered "divine works", although most of their authors relate to some form of divine intervention or revelations in events related to within the books.
The difference between this body of canonical work as representing only 24 books, and its form when incorporated into Protestant Christian scripture as the "Old Testament" is that the books of the Prophets in Hebrew Scripture have the 13 'minor' prophets (from Hoshea to Malachi) grouped into a single book. Furthermore, there is no separation into 2 parts in Hebrew scripture for the Book of Melachim (Kings), nor the Book of Shmuel (Samuel), whilst Ezra and Nehemia are individual books.
In traditional, or Byzantine (Eastern Orthodox) or the later Catholic Bibles, the 'deuterocanonical' works are included, with variations of which ones.
All of these extra books were gradually discredited and rejected from Jewish (Judean) Scripture by the Knesset Hagadol - The Great Assembly of Sages and Rabbis (empowered during +/- 400 BCE to 70 CE) and the later Sanhedrin (70 CE to almost 400 CE).
Most Deuterocanonical or Extra scrolls/books would actually have been lost were it not for translations of the Hebrew Bible in its then current form at the timeline of 200 BCE made by 70 Jewish, Hebrew and Greek-speaking Scribes for the Great Library of Hellenistic King Ptolemy in Alexandria, Egypt.
The Mishna, Tosafta, Breita, Talmudand many later books and articles, ending in the 'Shulhan Aruch' written between 1,900 to 500 years ago are not considered or intended to be seen as Holy Scripture. They represent the rulings of Jewish scholars and sages written as interpretations of the ancient and sometimes ambiguous language in the Torah.
Commandments placed on observant Jews by these interpretive works are called in Aramaic "Mitzvot De'Rabanan" (Rabbinical commandments) usually referred to as the "Oral Law".
This entire body of work of the Oral Law is rejected outright by a small but more than 1,100 year old Jewish sect called the Karaites (Literal readers), who see only the 24 books of scripture themselves and the commandments contained within them as worthy of following. They dispute many Oral Laws as in direct contravention of or at odds with, what they interpret as clear unequivocal commandments in Torah.
To the Karaites too, the Only "Divine"Holy Books in the Biblical Canon for the Samaritans are again - theTorah - The 5 books of Moses.
The chronology of the Hebrew Canon can be confusing, as books after the Torah included within it were only usually 'approved' for inclusion some considerable time after the events they relate to and more specifically, edited following the babylonian exile of Judea (586-516 BCE).
An example of this can be seen in the Canon of the Samaritans. The Samaritans ("Shomronim") after the fall of Samaria to Assyria were tainted by the residual and later successfully independent and thriving Southern Israelite Kingdom of Judea, as being descended from a foreign pagan people from eastern Mesopotamia who were exiled from their homelands and forced by the Assyrians who conquered them, to re-settle and make their lives in the hills of Samaria and to a lesser extent in the valleys of Galilee, from which the Assyrians had previously exiled much of 10 of the 12 ancient tribes of Israel, following the conquest of the northern Kingdom of Israel between 722-720 BCE.
The Samaritans themselves reject this Judean definition as a slander and claim direct descendancy from the Israelite Tribes of Ephraim and Menasseh - something borne out by DNA analysis among their Cohanim (Priests).
Nevertheless, the most important Holy Books for the Samaritans is again - the Torah - The 5 books of Moses. The books of the Prophets are seen as later works by them, not carrying the Divine Authority.
The Samaritan "Torah" remains unchanged since the time of the Northern Kingdom of Israel - the 10 tribes who seceded from the United Kingdom of Solomon following his death. They use the original Israelite alphabet of the First Temple period and earlier, never having adopted the later Judean script used by most Jews today, which was introduced following the Return to Zion from Babylonian exile. The Samaritans furthermore reject the importance of Jerusalem and Mount Moriah, believing certain events not to relate to Zion in Jerusalem but to Mount Gerizim in Samaria.
Although a tiny sect following persecution by Byzantines and slaughter by Crusaders, the Samaritans have the same 5 books of Moses as Jews, identical to this day, 2,731 years after the Nothern Kingdom of Israel was destroyed by Assyria.
In summary, for all branches of Jews, the 5 Books of Moses are the most Divinely Holy Books - The Torah.
All else is sacred but secondary and the product prophets; not dictated directly by God to Moses on Mount Sinai.
By learning it and observing its laws.
All Jews and most Christians honor the Old Testament as canonical.
The jewish book of sacred texts is called the Torah
The Torah
Yes.
Judaism
Christians consider the New Testament a sacred text, while Jews do not. Apex
Judaism is not a sacred text, it is a religion and that religion happens to have a sacred text. To learn more about Judaism's Sacred Text, read the Related Question.
No. You can read more about the sacred text of Judaism at the Related Question below. Yahweh is the archaeologists' approximation of the Jewish God's name, although nearly all religious Jews regard "Yahweh" as entirely inaccurate.
"Important" is a opinion
The Torah.
The Holy Bible is the sacred text for Christians.