“When you take this people out of Egypt,” said G‑d to Moses when He revealed Himself to him in a burning bush at the foot of Mount Sinai, “you shall serve G‑d on this mountain.”
It took seven weeks to reach the mountain. The people of Israel departed Egypt on the 15th of Nissan (the first day of Passover); on the 6th of Sivan, celebrated ever since as the festival of Shavuot, they assembled at the foot of Mount Sinai and received the Torah from G‑d.
The Kabbalists explain that the 49 days that connect Passover with Shavuot correspond to the 49 drives and traits of the human heart. Each day saw the refinement of one of these sefirot, bringing the people of Israel one step closer to their election as G‑d’s chosen people and their receiving of His communication to humanity.
Each year, we retrace this inner journey with our “Counting of the Omer.” Beginning on the second night of Passover, we count the days and weeks: “Today is one day to the Omer”; “Today is two days to the Omer”; “Today is seven days, which are one week to the Omer”; and so on, till “Today is forty-nine days, which are seven weeks to the Omer.” Shavuot, the “Festival of Weeks,” is the product of this count, driven by the miracles and revelations of the Exodus but achieved by a methodical, 49-step process of self-refinement within the human soul.