Deuteronomy 6:13 states:
Revere only the L-RD your God and worship Him alone, and swear only by His name.
Rambam in Sefer Ha-Mitzvot derives three different fundamental biblical commandments from this verse. The first one entails the admonition to fear God. How is this expressed? As words play such an important part in human behavior, endeavor and communication, the first step in establishing fear of God entails not glibly or flippantly mentioning the Name of God. Rambam utilizes a hypothetical Talmudic position that is actually rejected by the Gemara to fortify his case. Although Rambam recognizes (and indeed states) that the specific Talmudic hypothesis he cites is rejected, its fundamental premise, i.e., the overriding importance of establishing the Fear of God as a basic Jewish principle, remains. This Maimonidean passage is quite difficult, both in the original and certainly in English translation. It entails the Rambam shifting back and forth from citations of the stages of a relevant Talmudic passage, and providing interpretations of the points that underlie each of the stages.
Rambam’s words (Positive Commandment #4: Fear of God) speak for themselves. (My translation comes from Charles B. Chavel [trans.], Moses ben Maimon: The Commandments [London, Jerusalem and New York, 1967], Vol. I [Positive Commandments], p. 5, with modifications.) Rambam writes:
By this injunction we are commanded to believe in the fear and awe of God (exalted be He), and not to be at ease and self-confident but to expect His punishment at all times. This injunction is contained in His words Revere (only) the L-RD your God (Deut. 6:13; 10:20).
The Gemara of Tractate Sanhedrin (56a) discusses the verse (Leviticus 24:16) If he blasphemes (Hebrew, nokeb) the name of the L-RD, he shall be put to death. (The Talmud raises a hypothetical question, asking) “Perhaps the word nokeb should be taken to means “pronounced” (rather than blasphemed), as we find elsewhere (Numbers 1:17) The men that were pronounced [=designated] by name. [And in that case] the requisite admonition [for such a punishment] would be derived from the verse Revere only the L-RD your God.”
That is to say, (The Rambam interjects his own words here) the verse If he blasphemes(Hebrew, nokeb) the name of the L-RD, he shall be put to death might be understood as meaning that one who merely mentions the Name of the L-RD, without committing blasphemy [would be put to death]! If you ask, “What sin is there in that?” we reply that such a one abandons the fear of the L-RD, for it is part of the fear of the L-RD not to pronounce His Name in vain.
The Sages (in the following passage at Sanhedrin 56a) answer this question, and refute the view involved in it, as follows: “First, in order to constitute blasphemy [that would incur the death penalty] the Name [of the L-RD] must be used [in such a way that it might be represented as both the agent and the object of the blasphemy], and in this instance [of merely pronouncing the Name of the L-RD] the condition is absent.”
That is to say, (the Rambam himself interjects again and continues), [to incur the death penalty, the accused] must be guilty of blaspheming the Name [of the L-RD] in His own Name, just as the Sages say, [by substitution of a human name for God’s Name]: let Jose smite Jose.
Moreover, (the Rambam now cites the conclusion of the passage in Sanhedrin), the admonition that you cite is in the form of a Positive commandment, and it is an accepted principle [of Jewish law] that such an admonition is invalid.
That is to say (once again the Rambam now is speaking in his own voice), your suggestion that a prohibition against the mere pronouncing of the Name of God can be indeed derived from the verse Revere only the L-RD your God is inadmissible, because that verse in a Positive Commandment, and a prohibition cannot be based upon a Positive commandment.
The Rambam concludes: Thus it has been made clear to you that the words Revere only the L-RD your God lay down a Positive commandment.
Oftentimes, the conceptual substructure of a Talmudic passage is illuminated precisely by an opinion that is rejected, albeit for technical reasons. This might be the case here as well. To be sure, the point of the Gemara’s discussion on one level is simply to claim that positive language of Revere only the L-RD your God cannot be the source of a negative prohibition (in this case, one that would have incurred the death penalty). But on a more fundamental level, the very fact that the Talmud was willing to even consider this shows the overriding importance of the fear of God as entailing repercussions in our verbal expressions, and the supreme value of the concept of Fear of God in general. This might be another reason why the Rambam included the technical discussion of the Gemara in Sanhedrin in his remarks.
As the author of the early fourteenth century popular work Sefer Ha-Hinukh noted (cited by Rabbi Chavel in his comments), not only the first three commandments (to know that there is a God, to affirm the Unity [=absolute Oneness] of God and to love God) are binding for all time, and are subject to no limitations whatsoever as to time, occasion place or person, the fourth commandment, to fear God, is absolutely unlimited as well. In the secular, throwaway, superficial, artificial culture of the beginning of the twenty-first century, it is often hard to attain a sincere and profound fear of God. The first step is to recognize its universality of scope in the life of a Jew. I have set the L-RD always before me (Psalms 16:8). The operative word is always. We must all try as hard as we can to attain that goal during our lives.