Musar על מלכים ב 12:3

This type of fear is not so easy to attain, for it will arise only out of knowledge and thought, [namely] by contemplating G-d's exaltedness, blessed be He, and the lowliness of man. All these things are outgrowths of the intellect which understands and attains insight. This is the fear we described previously in Piety, setting it as the second part of one of the divisions of Piety.