What is the effect of the allusion to the Israelites when the narrator tells us that the expression of Grandison and his family as they looked back at the colonel "was not one of longing for the fleshpots of Egypt"?

It reminds the people to put the past to the past.

Explanation:

The statement "was not one of longing for the fleshpots of Egypt" refers to a Holy Bible account believed by Christians of the exodus of the children of Israel from Egypt. They had been held there as slaves for many years. As their God finally delivered them, their journey led them to follow a course that lay in the wilderness where there was no food or water. Because they were faced with adversities in the desert, they often complained and longed for the food in Egypt. In essence, the statement tells us to put past behind even though there were glorious days associated with it.