Tanya Chapter 33 part 1

If you are feeling weary and need extra joy, think about this: the idea of Hashem's true unity.  Hashem fills all worlds, spiritual and physical. Indeed, this entire world is filled with His glory, and everything has no value at all relative to Him. Let us picture how letters have no existence of their own within the essence of the soul, and how light has no existence at all while still within the sun. With this, we can understand how the world and everything in it, being contained with the Infinite One, has no existence of its own, and all there is is Hashem.