Baal HaSulam, “Matan Torah” (The Giving of the Torah), Section 17: From all the above, we can understand one of the most perplexing phrases of our sages: “All of Israel are responsible for one another.” This seems to be completely unjust, … But according to the above said, we can understand their words very simply; we have shown that each of the 613 Mitzvot in the Torah revolves around that single Mitzva: “Love thy friend as thyself.” And we find that such a state can only exist in a whole nation whose every member agrees to it.
We truly will have nothing to wait for and no hope that we can reach such an intensity of connection that is called love of others from our egoistic state, even though we have a group and study, unless we work in a dimension called the entire nation.
There must be an integration of very many connected desires here in which each one discovers his unique character, and then, to the degree of the full mutual integration between them, it will be possible to reach such a powerful desire that will attract the Light that Reforms, bringing them the quality of love.
The sons of Jacob were unable to reach this love, this intensity of desire, as long as they were closed within their family, and there was even hatred among the brothers, which testifies to the intensity of the desire required for correction. This is because each one had a different mother, his own share in the house of his father, and his own character.
However, even this was not enough for their connection, beyond rejecting each other, which would give them a fulfillment called love. Only when the great ego called Pharaoh was added to them and after they had gone through 400 years of the Egyptian exile and discovered all the levels of the ego, was the intensity of the separation sufficient for them to be called a nation instead of a group.
The idea here is not quantity, but speaks only about quality. Therefore, after they received additional ego, additional density, they began to call themselves a nation and merited to receive a means to make a correction that became imperative for them. This is because they no longer could correct anything themselves as brothers who felt themselves to be members of one family before their entry into Egypt.
With the exodus from Egypt and the heaviness of heart, after they took all the vessels of the Pharaoh, they already began to require the Torah.
From the 5th part of the Daily Kabbalah Lesson 5/27/14, Writings of Baal HaSulam