Дварим 6:13 Галаха: Arukh HaShulchan, Mishneh Torah, Foundations, Mishneh Torah, Positive Mitzvot & Sefer HaMitzvot

We are also commanded to fear the Blessed One, as the verse states (Devarim 6.13): "The L-ord your G-d you should fear", and here are the words of the Rambam concerning this trait in Sefer haMitzvos, mitzvah 4: "He has commanded us to be consciously aware of His exalted presence, and to tremble before Him, and not be like the heretics who presumptuously follow their own hearts; rather we should be concerned and mindful of His corrective punishment at all times, which is a consequence of sinful behavior. This then is the meaning of "The L-ord your G-d you should fear." That is his comment in the above source. In his great work (the Mishna Torah), in the beginning of the second chapter of the fundamentals of the Torah, he writes thus: "What is the path towards love and fear of G-d? When a person contemplates the wondrous actions and creations of G-d, and he sees in them wisdom without end or measure, immediately he loves, praises and glorifies Him. He also experiences a great desire to know his great name [TO KNOW HIM?], as Dovid has said: "My soul thirsts for the L-ord, the living G-d". When he continues to think about such matters, he has an immediate reflex to shrink away, and he experiences a fear and trembling, realizing that he is a small and inconsequential creation, with little intellect compared to the One of complete knowledge. Dovid has also stated regarding this: "When I see the heavens, the work of your fingers, I ask 'what is man that you take notice of him'?" Until here is his language. As can be seen, in the Sefer haMitzvos the explanation of 'simple fear' is fear of punishment, while here the Rambam refers to a higher fear, which is fear from the recognition of G-d's great loftiness. On this subject the Sifrei (Dvarim, 32) has stated: "There is no love in fear's place, nor fear in love's place, except for that of G-d alone." (see there). This means to say that fear and love are opposites, but through fear of G-d's vast loftiness they can dwell together, that through the recognition of the great, exalted stature of the Blessed One he is feared with an 'enlightened fear', and he is loved with all of one's heart and soul.

It is mandatory to love and fear this Glorified and Awe-inspiring God, for it is said: "Thou shalt love the Lord thy God" (Deut. 6,5); and as it is said: "The Lord thy God thou shalt fear." (Ibid. 6, 13).

To fear Him, as it is said, “The Lord, thy God, shalt thou fear” (Deut. 6:13; 10:20).