The larger and more material an object, the greater its shadow.
The same is true of G-d’s glory. The material obstructs the spiritual and casts a shadow.
When you are bound to an emotion or desire, it obstructs G-d’s glory and casts a shadow. G-d’s light is then hidden from you. But as you nullify these emotions and desires, you also remove this shadow. And as the shadow departs, the light of G-d’s glory is revealed.
Reb Natan, Sichot HaRan #136
From Rebbe Nachman’s Wisdom, Rebbe Nachman