Answer: The role of the teacher is to correct the student, and the role of the environment is to evoke the egoistic desire in him, not for the corporeal filling but rather for the spiritual filling.
There are two systems: the system of the uncorrected desires, the left line and the system of corrections, the right line. (Although it is clear that everything is run from above and designated for correction).
The teacher is on a higher level since he passes the Light downward to the students and for him the good and the evil come from one source. With regard to the student, which means on the lower level, the good and the evil are perceived as coming from two different sources, a good one and an evil one.
The teacher’s goal is to pass the Light to the student by the help of the study and the Creator, so that it will correct him and the good and evil will become one whole for him. This means that on his current level, the student will reach a feeling that “There is none else besides Him, the good and the benevolent.” Thus he ends the current level and goes on to the next level, and so he rises time after time.
It turns out that all the components have to be divided into two parts: the right line and the left line. And who are you? You have to try and reach the middle line, the upper level, in which there is no good or evil and where there aren’t many factors, but rather, everything converges into one: the group, the study, and the teacher—everything belongs to the Creator, and there is none else besides Him.
From the 1st part of the Daily Kabbalah Lesson 12/12/12, Writings of Baal HaSulam