The 4th mitzvah is that we are commanded to establish in our minds fear and dread of G‑d (exalted be He); that we not be calm and nonchalant, but be constantly concerned of imminent punishment1 [for misdeeds.]
The biblical source of this commandment is G‑d's statement2 (exalted be He), "You shall fear G‑d your Lord."
At3 the end of tractate Sanhedrin4, there is a discussion of G‑d's statement5 (exalted be He), "Anyone who is nokev (curses) G‑d's Name shall be put to death." [The Talmud asks:] "Perhaps the word nokev means, 'utters,' as in the verse6, 'Who were mentioned (nikvu) by name'; the prohibition7 being the verse, 'You shall fear G‑d your Lord.' "
The meaning of this question: "Perhaps the verse, 'nokev G‑d's Name' means merely uttering G‑d's Name even without a curse. And if one wonders 'What prohibition can there be in this?', it is [the prohibition not] to erase one's fear of G‑d; because included in fear of G‑d is not mentioning His Name in vain."8
The Talmud answers this question and rejects this approach as follows: "First of all, [in order to be punishable by death,] the person must have used 'one Name against another,' i.e. cursed one of G‑d's Names with another of G‑d's Names, as in the saying, 'Let Yosi strike Yosi,'9 and [if he merely mentioned G‑d's Name in vain,] he did not fulfill this condition."
[The Talmud continues:] "Furthermore, this prohibition is stated as a positive commandment, and cannot technically serve as a prohibition."
This means that the suggestion, "the prohibition is from the verse, 'You shall fear G‑d,' " is incorrect, because this verse is a positive commandment, and a punishment can never be based on a positive commandment.
This passage clearly indicates that "You shall fear G‑d," is a positive commandment.
