The horizon is the edge of mystery. We do not know what lies beyond it, and it does not matter how high we reach into the sky, we cannot see beyond that rim. This is the mystery we have inherited from the Divine, the reminder that we are but a part of the world and that, no matter the power and expanse of our dominion, we will never see everything.
As you ascend through the realms of enlightenment, you will not escape the horizon, and this liminal reminder will continue to haunt you through your ascension. At every stage and past every threshold, you will see that line that marks the edge of perception, and you will know that you are still finite.
This is the simplest definition of God: He Who Is Without Horizon.