To the left is the commandment:
And now, O Israel, what does G-d your G-d
ask of you, but to fear…. (Deuteronomy
This is the commandment to fear (yirah) G-d, or to be constantly in awe of Him. This is not referring to the fear of punishment. Although useful to fall back on as a means of keeping oneself from sinning if he is unable to arouse any deeper motivation, fear of punishment is not really considered serving G-d Himself. For if one performs commandments to avoid punishment, he is not doing them for G-d's sake, but rather for his own interests.
The mitzvah of fearing G-d begins with the fear of severing the bond of love with Him, and therefore flows naturally out of the previous commandment. If one truly loves G-d, he does not want to do anything that would separate him from Him, i.e., anything prohibited by the Torah.
At first, this fear is not even conscious; it is just a natural component of one's love for G-d. Eventually, however, when one has well-integrated his love of G-d into his daily life, he begins to sense the initial infatuation wearing off; his fear then becomes that of losing his emotional involvement with G-d simply due to his own stagnation. Cognizant that, as we said above, love of G-d is a product of one's awareness of His unity, this fear inspires him to transcend his present plateau of consciousness and seek newer insights in his conceptualization of Divinity. Fear thus allows one to transcend the limitations of his finite consciousness, in the process transmuting "love as water" (i.e., natural, pleasurable love) into "love as fire" (i.e., impassioned, unconsummated ardor), ever increasing the passion of love. As one ascends from level to level, each level of new-found love in turn becomes "second-nature" to him, and again the fear of lapsing into the rut of complacency spurs him on to seek higher levels of insight with which to fan the flame of love. Thus, fear works together with love, the two together becoming the "wings" of the soul (Tanya, ch. 40, quoting Sha'ar HaYichudim 11) which constantly elevate all one's good deeds, prayer and learning.
Implied in fear of G-d is the fear of approaching Him too closely, lest the soul be annihilated in the Divine ecstasy of its passionate love for Him. This would negate G-d's will, for He created each being with a unique purpose in life, which cannot be fulfilled by any other being. Submission to G-d's will thus means restraining one's ecstasy as much as is necessary in order to remain alive and continue to fulfill his life's mission. Thus, fear creates spiritual equilibrium, left (fear) balancing right (love).