Answer: We can long for something that we never had and not necessarily for something that is lost. I can long for some special car that costs a lot of money. This means that I feel pain because I don’t have the Light and constantly feel a hunger, a deficiency, a desire for it.
It can also be interpreted as longings for a past filling since we have its Reshimo (reminiscence). We don’t awaken to anything if a new Reshimo isn’t wakened in us because we are in a closed system of all of reality. There was a desire to receive that was shattered and all its parts drew away from one another, but there is a chain of Reshimot in each part that should recreate its connection with the other parts, until they are all connected into one whole vessel.
If we feel a yearning, if we feel sorry about something or long for it, then it means that we already had it before. Whatever I can imagine stems from the shattering of the vessels. Otherwise it couldn’t be revealed, not in our feelings, not in our mind, and not even in our imagination.
From the Preparation to the Daily Kabbalah Lesson 2/25/14