Institution of reading the Torah.

The commandment to study the Torah is a fundamental commandment, of which all other mitzvot depend. However, the Torah did not set a fixed time for the study, because the mitzvah to study the Torah has a permanent character, as it says: “You will meditate [the book of Torah] day and night” ( Jos 1: 8). In order to frame the link between Israel and the Torah, Moses therefore decreed that a reading of the Law should be done on Shabbat, as well as on Monday and Thursday in the morning; in this way, the people do not remain three days without hearing the Torah (Maimonides, Tephila 12, 1).
Our sages say that this decree was taken after the episode reported in the Exodus: “They walked three days in the desert and found no water” (Ex 15, 22). Moses our master and his disciples, the elders and the prophets, understood that the thirst came from the fact that for three consecutive days Israel had not publicly applied to the study of the Torah (Baba Qama 82a). The Torah is compared to water; for just as water gives life to all living things and all vegetation throughout the world, so does the Torah enliven the soul. And since the children of Israel were somewhat detached from the Torah, the springs also ceased to spring. Of course, it may be supposed that the sages of the generation continued to study during these three days; but what is meant here is the fact that for three days the people of Israel did not worship the Torah as a collectivity. So it was decided to institute a public reading of the Torah every Monday, every Thursday and every Shabbat, so that never more than three days pass without Israel hearing the public reading of the Torah.
Ezra the scribe also decreed that when reading the Torah on Monday and Thursday, three of the consecrated persons would be sent to the sefer-Torah, that each of them would read at least three verses, and that the sum of the verses read on the occasion of the three cumulative ascents would not be less than ten verses (Baba Qama 82a, Shulchan ‘Aruch, Orah Chaim 137, 1-2).