Why does the Torah consist of 5 books? We can infer from the Zohar that the 5 Books of the Torah correspond to the 5 levels of the human soul. These levels of the soul are Nefesh, Ruach, Neshama, Chaya and Yechida.

In the womb, the Divine soul is called Nefesh, from the root Nofash, 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 a man or a woman becomes obligated to perform Mitzvot, G-d introduces the Yetzer Tov, the 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 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 the body, only then can he conceive of G-d as the One and Only Power, and then his soul enters the sphere of Yechida. 

The Midrash in Vayikra Rabba explains that the soul is a part of G-d as it says in Devarim 32:9, "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 fibre of the body,  so too G-d's Presence permeates 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 the affairs of the mundane world but maintains His purity.

Nefesh corresponds to the Sefer Bereshit as it says, "Vayehi Haadam l'NEFESH Chaya", "And the human became a living soul". Ruach is connected to Sefer Shemot,

because in Sefer Shemot we received the Torah which is our Ruach. Neshama represents Sefer Vayikra, because Sefer Vayikra teaches about atonement through the Korbanot, which attain survival for the soul. Chaya symbolizes Sefer Bamidbar for in Midbar Kadesh we received new vigor and vitality of Kedusha. Yechida relates to Sefer Devarim as it says in Devarim 32, "The Rock, His work is perfect. All His ways are just; … and there is no evil" Realizing this truth is the level of Yechida, which is the highest level of the soul.