Condensed from Ein Ayah, Shabbat 9:42
Gemara: [We continue with initiatives of Moshe Rabbeinu that Hashem agreed to.] Moshe separated himself from his wife. From where did he derive this? He followed the reasoning of a kal vachomer. If about Israel, who Hashem spoke to for only a short time and the time was set, still the Torah said, "They shall not get close to a woman" (Shemot 19:15), I, to whom Hashem speaks on an ongoing basis and the time for this is not set, it is all the more clear [that I should separate myself from women]. How do we know that Hashem accepted this? [It says in the Torah, "Go tell them: Return to your tents" (Devarim 5:26). And then it says: "And you (Moshe), stand here with Me" (ibid. 27). Some say that it is derived from [that which Hashem said about Moshe]: "Mouth to mouth I speak to him" (Bamidbar 12:8).
Ein Ayah: The laws of morality, in all of its aspects, whether regarding characteristics or in the lofty holy elements of moral content, find expression in two forms, wherein one is more internal than the other. These are: the form of commandments to act in a certain way and a great natural status that one possesses.
The obligation to do something is great in its loftiness; it appears from a place that is much higher than the level of man. The natural greatness of man is great in its depth and the impact it has, as it connects to a person’s essence.
In regard to every revelation, whether it comes to the person by means of wisdom and recognition or whether it appears to him through prophecy, there is opportunity for the two types of acceptance. When a person who is ready for it receives light, it is apt to change his characteristics from those of obligation to those of nature.
The general, lofty revelation that set the foundation of Moshe Rabbeinu’s personality and enabled his prophecy to be above that of anyone who preceded him or would follow him, had to have had elements of both types of characteristics. It had both the matter of obligation and that of the nature of the greatest of all spiritual people of all choice people.
Thus, on one hand, Hashem commanded Moshe: "And you, stand here with Me" (Devarim 5:27), as opposed to that which the others were told: "Return to your tents." The natural restriction on Moshe was a result of the fact that Moshe was on the level that Hashem spoke to him "mouth to mouth." This cannot exist unless Moshe was on such a high level that he was beyond being drawn to physical relationships, and that is why [he felt that he could not have such a relationship and Hashem agreed]. That separation was a result of the prophecy. This high level applied also to any personal study of such a uniquely elevated human being, to whose ideas Hashem agreed, both by means of a commandment and as an expression of his natural greatness.