Why was the Torah so important to the people?

Answer 1

The Torah is like water; all life needs it.

Guidance, teaching and spirituality is one of the fundamental aspects of humanity and, as such, is essential for the healthy functioning of any human being as part of society.

Among other things, what the Torah did was lay down the foundations for Judaism's legal, ethical and religious works, etc; for this reason, it can be considered somewhat equivalent to the Napoleonic Code (which stems from Roman Civil Law) or the US Constitution (from the Native American Iroquois/Haudenosaunee League Of Six Nations), etc. all of which are guiding principles for vast amounts of people.

However, the root of the word "torah" is "teaching/guidance" as opposed to strict "law", so it should be noted that "Torah" can denote both the written text Torah Shebichtav ("Torah that is written") as well as the oral tradition Torah Shebe'al Peh ("Torah that is oral"), with the oral consisting of traditional interpretations and expansions of the written which were handed down by word of mouth from generation to generation and which are now embodied in the Talmud and Midrash.

Answer 2

The Torah increases our reverence towards God; crystallizes, strengthens and codifies our beliefs; insures our awareness and knowledge of our history; and provides powerful impetus to be ethical.
It makes us stand in awe of God, while also providing optimism and comfort through the prophecies of redemption. It inspires us to strive for holiness and informs us how to pray and to approach God's presence.
It gives us a great deal of general information, guidance and advice.
And it sets detailed laws, practices and traditions for us.

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The laws themselves have various reasons. Some (such as the Passover) serve to reenact or commemorate events of our history.
Some (such as saying the Shema prayer) serve to reiterate our belief in God.
Some of the laws (such as those of ritual purity and kosher food) serve to sanctify us.
Some (such as the laws of torts) serve to maintain an orderly society.
Some (such as the law against breaking a vow) serve to prevent bad character traits.
Some (such as the command to offer help) serve to engender good character traits.
And all of the commands serve to subjugate us to God's will (especially those commands for which no explanation is easily apparent).

Some examples of the commands:
Putting on Tefillin (a.k.a. phylacteries) in the morning
The sukkah-booth during Sukkot
Avoiding leavened products in Passover
Not eating on Yom Kippur
Not working on Saturday (Sabbath)
Paying workers on time
Marital rights for one's wife
Counting the days of the Omer
Returning lost objects when feasible
Wearing the tzitzith-garment
Learning Torah
Marrying and having children
Educating one's children in Judaism
Giving tzedakah (charity)
Honoring one's parents
And many more.

Note that the Torah "as is" isn't exactly what Judaism observes. Rather, It's the Torah together with the details provided in the Talmud, which is the Oral Law that was handed down together with the laws of Moses. Otherwise, the verses of the Torah often lack enough detail to be fulfilled as is.

See also:

What are some facts about Torah-scrolls?

What are the key teachings of Judaism?

What is the history of the Hebrew Bible?