A nineteenth century wit once said “If ghosts have clothes, then clothes have ghosts.” Actually, he missed the mark entirely. Spirits wear clothes because clothes are simply part of the mental image they brought with them from their earth lives. A spirit’s clothes are really just another part of its spirit body. Remember that a spirit’s environment, including its own body image is first formed in its imagination. Just as most of us would not venture outdoors without clothes, neither would most spirits.
As spirits evolve to higher and higher levels, first their clothes and then their bodies change becoming more and more radiant. As they reach the upper levels of the fourth plane, they begin to lose their “physical” appearance because their bodies become more and more irrelevant to their perceived needs. Once they enter into the highest planes, they no longer need any bodily appearance at all and think and act exclusively with their minds, although they may don spiritual bodies to perform special functions. A part of spiritual evolution is the voluntary abandonment of even the illusion of matter and the assumption of pure consciousness.
Note: According to Frederick Myers, once a soul reaches the fourth plane, (the first plane above the planes of illusion), its imaginative forms begin to become so refined and ethereal that by the time it has fully evolved on that plane, both its spiritual body and its environment have become quite literally “unimaginable”.
Human Spirits that devolve in a downward direction and sink into the winterlands and below bring their mental status with them and their internal ugliness is visible to higher spirits. The lower they sink, the uglier they become. As they sink into the lower realms, their interactions with other spirits of their status become more and more violent, and this takes a toll on their mental state and, consequently their appearance.
Remember that spirits do not have physical bodies, and thus cannot acquire real injuries, however they perceive the injuries from their interactions with other entities to be real and they carry these memories for as long as they remain within these lower planes. Therefore, their appearance, already ugly due to their base natures, deteriorates even further. If one of these sub-human entities finds its way back to the earth sphere, usually because of energy supplied to it by an evil living person, it might look to you like a demon or even Satanic in appearance…all of which brings us to the subject of zombies.