Tzimtzum: צמצום
The Divine Name associated with the Sephira קתר, Keter, is אהיה, which may be translated as I am becoming what I will be. As קתר is associated with Divine will, we can gain further insight. It is the Divine will that the Divine should be understood to humankind as a becoming. That is, for us, the "beingness" of the Divine is its "becomingness."
Now "beingness" is the essence which is and "becomingness" is the essence which is to be. For the "beingness" of the Divine to be its "becomingness" means that the essence of the Divine is its quality of "revealingness," its quality of revealing its Divine nature.
But for a revealing to occur, there first has to be that which is not revealed and then it is revealed. That is, there must be a prior concealment. And this means that the dimension of time is a necessary dimension for the essence of the Divine to be experienced by us.
The essence of time is its order from prior to subsequent. This is the reason that the Torah begins with the word בראשית, which means in the beginning or with a beginning, for that which has a beginning exists in time. It is exactly this element of time that is the צמצום the contraction, the restriction. For in the Divine plenitude all time is simultaneous. But for us who exist in time, time is one moment followed by another.
For us, the entire Divine nature, as we can understand it, is contracted so that it can be squeezed through the pinhole of time and the separation of space, thereby making its concealment inherent in its beginning and its revealment possible through time, one moment following another. And this revealment is the essence of our living, for living means doing and making.
Each of us lives because we have a mission to fulfill. This mission involves doing or making revelations of the Divine for others and ourselves. We succeed in this mission when we are able to facilitate the experience of the revelation of the Divine nature, which is its beneficence. This experience is an experience of delight in our receiving the Divine beneficence by sharing with others the Divine beneficence given to us.