Why did the Jews have to leave Egypt with רכוש גדול? What was the significance of the Bnei Yisroel asking the Egyptians for silver, gold? (Shemos 11:2)
"After they will leave with a great possession"
To what was this referring?
The Great Possession was really the Torah!
But haShem asked Moshe to tell the B'nei Yisroel to request gold & silver vessels from the Egyptians to ensure that none of the less sophisticated members of the B'nei Yisroel would not underestimate the value of the Torah and therefore feel cheated! So He asked that they bring along material possessions.
But the true Great Possession they would get soon enough, on their way out, at Har Sinai!
This was in order for Hashem to fulfill his promise to Avraham found in parshas Lech Licha chapter 15 verse 14. וגם את הגוי אשר יעבדו דן אנכי ואחרי כן יצאו ברכש גדול.
From Chabad.org, a concept well-known in Chassidus (maybe someone can add the source):Why was it so important that the children of Israel should carry out the wealth of Egypt, to the extent that this was foretold hundreds of years earlier to Abraham as an indispensable component of their redemption?
Every creation contains a “spark of holiness” which embodies its divine purpose. When a person utilizes an object, force or phenomenon to serve the Creator, thereby realizing its function within G‑d’s overall purpose for creation, he “redeems” and “elevates” the divine spark at its core.
Every soul has its own “sparks” scattered about in the world, which actually form an integral part of itself: no soul is complete until it has redeemed those sparks which belong to its mission in life. Therein lies the purpose of galut in all its forms: the exile of the soul from its sublime origins to the physical world, and the various exiles that nations and individuals experience in the course of their history, impelled from place to place and from occupation to occupation by seemingly random forces. All is by divine providence, which guides every man to those possessions and opportunities whose “spark” is intimately connected with his.
As the father and prototype of all exiles, the Egyptian galut was a highly concentrated period of history, in which the foundations were laid for all that was to unfold in subsequent centuries. The material world contains 288 general “sparks” (each of which includes innumerable offshoots and particles); of these, 202 were taken out of Egypt, redeemed and elevated when the Jewish people carried off its gold and silver and used these to construct a sanctuary for G‑d in the desert (see Exodus 25–31).
Rabbi Sacks, in his book "Ceremony and Celebration" on the chapter about Passover brings a novel answer for this question, maybe someone can add it to this post, don't have the book w me...