To Fear G-d

Devarim 6:13 Hashem, your G-d, shall you fear, Him shall you serve, and in His Name shall you swear.

Devarim 10:20 Hashem, your G-d, shall you fear, Him shall you serve, to Him shall you cleave, and in His Name shall you swear.

By this injunction we are commanded to believe in the fear and awe of G-d, Baruch Hu (Blessed be He), and not to be at ease and self-confident but to expect His punishment at all times.

The Gemara of Tractate Sanhedrin discusses the verse, "he that blasphemes (nokev) the Name of Hashem, he shall surely be put to death" (VaYikra 24:16): "Perhaps the word nokev should be taken to mean 'pronouces' (rather than 'blasphemes'), as we find elsewhere, 'The men that were pronounced (nikevu) by name' (BaMidbar 1:17), the (requisite) admonition¹ being derived from the verse, 'You shall fear Hashem your G-d?'² That is to say, the verse, 'he that blasphemes the Name of Hashem,' etc., might be understood as meaning one who merely mentions the Name of Hashem, without committing blasphemy; and if you ask "What sin is there in that?" we reply that such a one abandons the fear of Hashem, for it is part of the fear of Hashem not to pronounce His Name in vain.

1. It is a principle of Rabbinic exegesis that no punishment is prescribed in the Torah unless a prohibitive warning or admonition has preceded it. E.g. ye shall do no manner of work in that same day (i.e. in Yom Kippur, VaYikra 23:28), provides the admonition; whatsoever soul it be that does any manner of work in that day, that soul will I destroy among his people (ibid., 30), prescribes the punishment.
2. Sanhedrin 56a

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