The Lubavitcher Rebbe on The Mystical Meaning of Seven

Nobody can deny that Rabbi Menachem Mendel Schneerson (05 April 1902~12 June 1994) was an extraordinary man. He possessed great wisdom and build the Chabad Lubavitch movement from a small remnant to what is perhaps the largest Hassidic group in the world. 

Almost every where one travels, people know of Chabad. Jews in every country, whether religious or not know that if trouble arises, the place to go is Chabad. I have heard many stories from "non-observant" Jews who became stranded in foreign countries, where embassy help was just not available. Each time the story was the same: "We called Chabad and they took care of everything for us" That this great work has continued to grow after the passing of the Rebbe, and without an official "rebbe" to lead the group is an indication of the leadership and charisma of  the seventh and last rebbe of the Chabad Lubavitch movement.

The Lubavitcher Rebbe gave this lecture "Bring Heaven to Earth" on  10 Shevat 5711 (17 January 1951). I have copied the explanation that goes with the video for your convenience.

The Sages state that "All Sevenths" are cherished. This is the reason, they explain, why Moses was the one who merited to bring Gds Presence into this world because he was the seventh from Abraham. The fact that the seventh is cherished indicates the greatness of the first. 

What was the unique quality of Abraham? Abraham served Gd with self-sacrifice. He called out in the Name of Gd, Master of the world the Sages explain: Not, he called out, but rather he brought others to call out. 

This self-sacrifice is expected from each of us in the seventh generation. Even if one feels no spiritual strengths within himself, he is nevertheless told: It is not by your own choice that you are the seventh generation you have the strength by the very fact that you are the seventh. You must realize how cherished you are, and how much has been invested in you. You will then fulfill your part in the mission to draw Gds essence into this material world

The Mystical Meeting of Seven "7"