These are the offspring of Aaron and Moses on the day G-d spoke with Moses at Mount Sinai: These are the names of the sons of Aaron, Nadab, and Abihu, Elazar, and Ithamar.Ch.3/1-2

Although Moshe had two sons, Gershom and Eliezer, they are not mentioned here. If only the offspring of Aaron are listed, why does the Torah say it is going to list the offspring of Moses as well? To answer this, the Sages teach us a profound idea. Since Moses taught the sons of Aaron Torah, it is as though he gave birth to them. In this respect, they are his progeny.

The Torah does not exaggerate. So how are we to understand that a teacher of Torah gives birth to his student?

The baby in the womb is in a very constricted environment, then out he comes into the big-wide-world. Mazel Tov! This is what the Torah does for his neshomah (soul). The Torah which is pure spirituality, connects him to his neshomah. Now it's a new world. People are creations of G-d. Nature is here by Divine Design. His day is filled with opportunities to overcome his physical desires. The neshomah can express itself through performance of the mitzvot (Torah commandments.) Likewise, his Torah teacher brings him from the world of physicality, constricted by time and space, to a world of spirituality, that which lies beyond time and space.

Rabbi Samson Raphael Hirsch teaches that this same birthing process occurred to us as a nation when we left Egypt and came to Mount Sinai. When we left Egypt, that was the physical creation of the nation. At Mount Sinai, we experienced our spiritual creation, with the receiving of the Torah. Pesach is the celebration of the former event; the approaching Shavuot will be the celebration of the latter.

All the countings of the Levites, which Moshe and Aaron counted by the word of G-d according to their families, every male from one month of age and up, were twenty-two thousand. Ch.3/39

Levi was the least populous tribe, numbering only 22,000, and that's including all the males from a month old and up. The other tribes, by contrast, had much higher numbers, even though their count started with twenty-year-olds. For example, the tribe of Yehudah was 74,600. Why is it that Levi, the most prestigious tribe---chosen for the Temple service and to be the teachers of Israel---was such a small group?

One answer is that G-d wanted to teach us an important lesson: In the service of G-d, it is quality that counts, not quantity. Levi, although the smallest in terms of numbers, were giants in their loyalty to G-d. This came to light at the Sin of the Golden Calf, when they alone refused to participate in the idol worship. For this they were raised up to be the most prestigious tribe, despite their low numbers.

And this lesson remains true today. Rabbi Yisrael Meir HaCohen (1839-1933), known as the Chofetz Chaim, used to say that G-d's map of the world looks very different from ours. Whereas on our maps, importance is determined by population, the biggest cities being the most prominent; on His map the biggest places are the centers of Torah. So on His map there may be small towns and villages that dwarf the much larger population centers. Because it's quality that counts, not quantity!

Sources: Tam VeDas from Rav Sternbach