Three Levels of Fear
Just as the flame of love possesses three levels of ascent to God–"with all your heart, and with all your soul, and with all your might"–so does its companion, fear, possess three levels (the two levels previously described and a third, even higher level, alluded to at the beginning of our discussion of fear):
The fear that our bond of love with God be severed corresponds to loving God "with all your heart." Recognizing the presence of our evil inclination–our inner potential to sever our relation with God–through the fear of God, we elevate this very potential to serve God. In the terminology of our sages, this level of fear is called "the fear of sin" (yir'at hachet).
The fear to approach God too closely, lest one become annihilated in Divine ecstasy, corresponds to loving God "with all your soul"–"even if He takes your soul." Though one is always ready to sacrifice his life for God, he must know and ever take to heart that God's will is that, in general, he remain alive on earth to serve Him. The very readiness to sacrifice his life for God's sake brings him to this level of fear. This level of fear is called "the fear of God's exaltedness" (yir'at haromemut). In direct proportion to the experience of "God's exaltedness" (which, if not balanced by fear, would result in self-annihilation, in the Divine ecstasy of approaching Him to become one with His exalted essence) must one experience "human lowliness," the recognition that "God is in heaven" and "I am on earth," to live here and perform His will on earth.
While "the fear of God's exaltedness" implies standing in awe of Him–in contrast to the first level of fear, "the fear of sin," which is actual fear–the ultimate state of awe in the presence of God is that of the next, highest level of fear, "fear of shame" (yir'at boshet).
"Fear of shame" is the experience of ever standing in the presence of the Infinite One, blessed be He, and feeling that as He is all and all is He; who am I?! This corresponds to the level of "with all your might," for here, as all is God, all is a manifestation of perfect, absolute Divine goodness and mercy. In existential shame, I thank Him exceedingly for every measure of life. Here, the sefirah of gevurah, whose inner experience is fear, reaches its essence, as gevurah means "might."
In general, "fear" implies "sensitivity." In Kabbalah, the left creates boundaries, identifying the other and separating oneself from the other in order to objectively sense the other's independent existence. A rectified left continues to nullify one's own ego and self-centeredness, for of all the emotions of the heart, fear most humbles one's ego. Thereafter, it is the left itself that totally overcomes separateness, in its continuous experience of God's omnipresence and omnipotence.