Thus, clearly, they did not know Joseph. In other words, they attained him only to the extent that they valued him in their hearts.

Therefore, they depicted the image of Joseph as they themselves were. Because of it, they did not know Joseph and the enslavement began. Otherwise, the righteous would certainly protect them and exile or enslavement would not be depicted to them at all (Baal HaSulam, Letter 10).

The sons of Israel were at a developmental level controlled by egoism, and they could not yet rise above it and approach Joseph.

Joseph is a very high-quality bestowal that could connect them. Since they did not achieve such a connection, they remained in exile.

Moreover, their acquaintance with Joseph did not give them any advantage. They were unable to use his power to leave Egypt.
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From the Daily Kabbalah Lesson 4/23/24, Writings of Baal HaSulam Letter 10

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