It is the first step of separation from the world (ʿālam). This is because the corporeal world is the first thing from which one turns away. To turn away from it is, in essence, to be separated from it. The order of manifestation in creation is not the same as the order of the great realms present in the world. The first thing to separate from the great world is earth, then water, then air, and then fire. When a human being separates from these elements, with his ruh (the spirit), he enters the sky of the dunya (the lower world).
Our shaykh (Ibn ʿArabī) says: When Allah the Exalted willed to elevate me in order to show me my names that are present in His Names, He first removed me from my place. And He elevated me with the Burāq that was present in my domain of possibility. He cast me away with all my elements. I could not discern whether He was pleased to befriend me or not. It was said to me: Your original father, whom Allah created from earth, He took him.
When I separated from the element of water, I lost a part of myself. It was said to me: You are a simple water.