The other two places are when Moshe sees the סְּנֶה (Burning Bush - Shmos 3:14) and at הר סיני (Mount Sianai - Yisro 19:4). In both those places the letter is full size. Rabbi Sorotzkin points out that at the Burning Bush, Moshe is being chosen for his mission. He will be appointed to the position of leader and must confront Pharoah and take the Jewish people out of slavery. It is inappropriate to think that G0d would "happen" upon a person and immediately appoint him to such a position. Indeed the initial message to Pharaoh commanded in Shmos 3:18, does indeed use the language of "happenstance", נִקְרָה עָלֵינוּ, this is solely so that Pharaoh could understand the message. The message to the Israelites uses the word "appeared", נִרְאָה, to shown that it is indeed deliberate. Thus, the calling cannot be minimized. It must be given its full worth and to do otherwise would cheapen the mission.
Similarly, the calling of Moshe to the mountain cannot be minimized either. He is about to get the Torah for the israelites. This from the beginning has been the entire purpose of the exodus. Again it must be shown in its full value and importance. Consider what is about to happen and the thunder annd lightning that will accompany the Voice of G0d as He gives the commandments.
Finally, we come to Vayikra. moshe is called to the mishkan (tent of meeting) in order to receive the instructions on how to inaugurate his brother as the High Priest and his nephews as the attending priests. He immediately rushes in to get the instructions and follows them exactly as he does honor to his brother. Here, at last, he is allowed to express his humility. Doing so will not diminish the honor of the task that he is about to do. Indeed it increases it, as he is showing that it is Aharon and his sons who must be honored in being able to take part in the sacrificial ritual and eat (when appropriate) from the meat. Moshe regards himself as only a conduit to do honor to them. Here, finally, he is allowed to diminish himself and present himself as less than the leader of Bnei Yisroel.
This teaches us a lesson about our times as well. The talmud has a principle that there are circumstances in which a person is forbidden to forgo any of the honor that is due him. This occurs in a situation in which it would diminish the mission if he were to do so. The mission is more important than the person. Rabbi Frand
told the story as follows:
There is a famous story which illustrates this point. Rav Chatzkel Abramsky, zt"l, once needed to testify in a case in which the Beis Din of London was sued by a shochet [ritual slaughterer] who had been fired. As the head of the Beis Din, Rav Abramsky had no choice, but to testify in secular court. His attorney asked him to state his name and his position. The attorney then asked, "Is it true that you are the greatest living halachic authority on the European continent?" Rav Abramsky said, "Yes. That is true."
At that point the judge interjected and said, "Rabbi Abramsky, is that not rather haughty on your part? I thought that your laws and ethics teach you to be humble." Without any hesitation, Rav Abramsky responded, "I know we are taught to be humble. But I am under oath."
The point of this story is that Rav Chatzkel Abramsky was aware that he was the greatest living halachic authority on the European continent. Recognition of his true status was not haughtiness.
Because he was called to testify on a matter of Torah Law, he had to accept and acknowledge his position as the "greatest living halachic authority". The talmud states
"If a Nasi wants to overlook his honor, his honor may be overlooked. If a king wants to overlook his honor, his honor may not be overlooked."As part of the discussion, it states that even though the king has declared that the honor can be overlooked, as a human being his honor can be overlooked, however, the honor of the kingdom and of the position that he holds will still be required the next second. Similarly, as long as it was required for the mission, Moshe Rabbeinu could not forgo his honor. It is only when the mission itself required that he act as an individual and subordinate himself that he could allow his humbleness to manifest.