The 16 expressions of forgiveness

Are we dust or divine? 

Or: What is the meaning of the divine presence having first been in a revealed state below?

There is a rule in halacha that "anything that we revert eventually to its original form is not considered to have really changed in the interim."

Since Adam is told, "you are dust and you will return to dust," one might think this rule applies. That all of our efforts to purify our bodies while we're alive are fruitless efforts, since it will revert back to its original state of "dust," negating the interim efforts and achievements.

The answer to this is that "ikar Shechina betachtonim haysa," "the main revelation of the divine presence was originally down here." Since Hashem says, "make for me a sanctified place and I will dwell amongst the people," the expression of divine dwelling becomes inexorably related to the existence of man. Just as the dwelling of Shechina was the true original state of existence, our purpose as the place of his dwelling is primal, since Hashem's choice is to dwell there and "I am Hashem I haven't changed."

This rebuttal to the "we are dust" idea is reflected in the concept of the "Luz" bone and the revival of the dead. The entire body will be rebuilt from this bone by the revival of the dead. "Rebuilt," specifically, since it will be reverting back to the original state and not created anew. The Luz bone does not derive benefit from this world (aside from Melave malka) since it reflects that unchanging original state of the dwelling of the Shechina.

From Likutei Sichos (Vov)