This is explained in detail giving the symbols which heretofore have remained secret and are now revealed in brilliance.
Bahir Verse 88. What is the meaning of the expression, "It rose in thought"? Why do we not say that "it descended [in thought]"? Indeed, we have said, "One who gazes into the vision of the Chariot first descends and then ascends." We use the expression [of descent] there because we say, "One who gazes into the vision (Tzafayat) of the Chariot." The Aramaic translation of "vision" (Tzafiyat) is Sechuta [meaning a covering, and alluding to the fact that one is looking down from above]. It is also written (Isaiah 21:8), "And he called as a lion: `Upon the watchtower (Mitzpeh), O God.'" Here, however, we are speaking of thought, [and therefore only speak of ascent]. For thought does not include any vision, and has no ending whatsoever. And anything that has no end or limit does not have any descent. People therefore say, "Someone descended to the limit of his friend's knowledge." One can arrive at the limit of a person's knowledge, but not at the limit of his thought.
Commentary: The chariot is the cycle of thought. The vision is thought itself in terms of lower thought and higher thought. The watchtower is our ability to observe thought while it is in motion. Thoughts decay, this is the lower form of thoughts. New thoughts arise, this is the higher form of thought. It says thought doesn't include vision because vision tends to be stationary, however when vision is in movement so too therefore is thought. It says thought doesn't descend which is true. Only the echoes of thought descend. It is these echoes or klippot that confuse us and cause the reactions we have called the ego. When thought is followed to its natural extension we experience the unlimited. What a story we are telling here. Wait it gets better, stay tuned.