Matt: 5:4 Blessed are they that mourn: for they shall be comforted. – testing the student’s willingness to surrender his desires.
Just as the student must empty his mind of opinion, so must he empty his heart of all desires and fears. The student must feel true contrition for the miserable state that he has gotten himself into. Like the Prodigal Son, he must have come to the realization on his own that his life is totally devoid of truth and goodness and be willing to give everything for the privilege of returning to his true spiritual state, if only as a servant.
We mourn that which is lost. How can we receive if we still have? When the ego realizes that it is nothing, has nothing , and is capable of nothing, there is great sorrow. Jesus is saying, as a way of testing the aspirant, ” You’re not worth camel dung.” Anyone coming face to face with this knowledge will mourn. This is the epitome of the spiritual principle, “Of myself I do nothing.”
The Mystical Christ 
I would like to elaborate on :”You’re not worth Camel dung”: is referring to our untransformed Ego, not our True Nature or Higher Self. .
Yes, Carolyn, that’s what it refers to. I’m so glad that you like these interpretations!