Love and Awe: Tanya Chapter 39

Rabbi Steinstaltz states in his commentary on the premier work of Chabad Chassidut, the Tanya:

Love and awe are wings that make a mitzvah 'fly' and raise it up from this world.  Just as a bird cannot fly without wings, so too it cannot fly with only one wing.  A person needs love and awe together in order for his or her service of G'd to rise up to heaven.  In truth, it is impossible for there to be true love without awe; when love is serious it is accompanied by awe, a worry that loss of the love will occur.