Vedanta holds that we do not get into the waker or the dreamer directly. We have to go through the sleeper. The deep sleep is like a corridor between the waking and the dream. In order to go from one state to another, I have to take that off and put this one on. This is what it means in the fifth mantra. Cheto-mukaha literally translates as a door of consciousness.
Swami Sarvapriyananda teaches one of the shortest and most profound upanishads accompanied by Gaudapada's Karika. This lecture covers Karika 1-5.