The Parshah of Vayelech (“and he went”) recounts the events of Moses’ last day of earthly life. “I am one hundred and twenty years old today,” he says to the people, “and I can no longer go forth and come in.” He transfers the leadership to Joshua, and writes (or concludes writing) the Torah in a scroll which he entrusts to the Levites for safekeeping in the Ark of the Covenant.
The mitzvah of hak’hel (“gather”) is given: every seven years, during the festival of Sukkot of the first year of the shemittah cycle, the entire people of Israel—men, women and children—should gather at the Holy Temple in Jerusalem, where the king should read to them from the Torah.
Vayelech concludes with the prediction that the people of Israel will turn away from their covenant with G‑d, causing Him to hide His face from them, but also with the promise that the words of the Torah “shall not be forgotten out of the mouths of their descendants.”
Source: chabad.org