Malchus

In Kabbalistic terms the sphere (and Sfira) in which we humans operate is called מלכות, Malchus. Malchus means monarchy, and this begs the question: What does Monarchy have to do with our sphere of activity?

The Gaon of Vilna explains that the primary function of Creation is for us to find the presence of God in Creation. Ultimately, it is our mandate to discover the God permeates the entirety of Creation, as much as that doesn't seem to be the case to the naked eye at the present time.

The concept of Monarchy demands that there be only one monarch and not more (אין שתי מלכים משתמשים בכתר אחד). God created all the forces that appear to oppose Him in order for us to ultimately come to the realization that there is no other. It is our activity in bringing about this revelation, that gives the name Malchus to our sphere.

The Greatest Accomplishment

We have mentioned before that God's purpose in Creation was in order to bestow good upon His Creations. The essential spark of Creation was His creating the ability to receive which had not previously existed.

It stands to reason then that when a person creates a situation in which he and/or others can be vessels to receive God's goodness, he has participated in the epitome of fulfilling the Will of God. 

Tohu

The concept of אין עוד מלבדו, (there is nothing other than Him) does not mean that Creation is non-existent and is a mirage. Rather, it means that as compared to Hashem, all is like nothing. His infinite greatness which is not diminished by Creation, cannot be conceived by any Creation.
As long as a person feels a sense of self, of ego, he is, by definition, incapable of comprehending the infinite existence of Hashem. This is the concept of תוהו, wondering and bewilderment, in that a person can know that Hashem is infinite, but can never fully comprehend that infinity.