Why does the Torah consist of 5 books? We can infer form the Zohar that the 5 books of the Torah correspond to the 5 levels of the human soul. These levels of the soul are 1) Nefesh 2) Ruach 3) Neshama 4) Chaya 5) Yechida.

In the womb, the Divine Soul is called Nefesh from the root Nofesh, resting, because before birth the soul has not yet been activated. At birth, the soul is called Ruach which means wind, because the soul is now free like the wind to soar in any direction.

When the infant starts to nurse, the soul is called Neshama from the root Neshima, the breath of survival, because nourishment is essential for human survival.

Until the age of Bar or Bat Mitzvah, the soul is still relatively dormant. When one becomes obligated to perform Mitzvot, G-D introduces the Yetzer Tov (Good Inclination), into the soul which activates it to serve G-D. Then the soul is called Chaya, the live one, because it receives new vigor and vitality.

When the soul finally comprehends that G-D is the one and only power in the universe, the soul is referred to as Yechida, the unique one and only. Most people never achieve this level of apprehension of G-D. This level of achievement is for the truly righteous who struggle all their lives to comprehend G-D in each and every event and attain the level of Yechida in this world. Thus, the Talmud in Chulin 7 states that a person does not even stub his toe unless G-D directly ordains it.

However, when an ordinary person dies and his soul is released from his body, only then can he conceive of G-D as the One and Only Power. Only in Olam Haba does his soul enter the sphere of Yechida.

The Midrash in Vayikra Raba explains that the soul is a part of G-D himself. As the Torah states in Devarim 32, "For G-D is a portion of His people". The Midrash continues to describe how the soul actually resembles G-D himself. Just as the soul permeates every fiber of the body, so too G-D's presence fills the entire world.

Just as the soul sees everything but yet is unseen, so too G–D sees everything but He remains unseen. Just as the soul is connected to the body, yet it preserves its purity, so too G-D is connected to this mundane sinful world but maintains His purity.

The Nefesh part of the soul corresponds to the book of Bereshit as it says, "And the human became LE'NEFESH Chaya". The Ruach part is connected to the book of Shemot, because in Sefer Shemot we received the Torah which is our Ruach.

The Neshma part of the soul represents the Book of Vayikra which teaches about atonement through the Sacrifices, which attain eternal survival for the soul. Chaya symbolizes the book of Bamidbar for in Midbar Kadesh we received new vigor and vitality of Kedusha.

The most exalted part of the soul is Yechida, related to the Book of Devarim as it says, "The Rock, His work is perfect. All His ways are just". Realizing this truth is the level of Yechida which is the actual unification of the soul to G-D.