"...Spiritualism has several different meanings, but it usually refers to a religious movement originating in the mid-nineteenth century. This movement has always stressed survival after death and communication with the dead by means of psychic mediumship. Claiming to embody a 'scientific' spirituality, Spiritualists reject many doctrines of traditional religions, such as eternal damnation.
Most known societies have believed in the possiblity of communication with the spirit world. One of the key notions of mainstream Spiritualism is the idea of spirit guides--disembodied helper spirits who are often deceased relatives. These guides resemble traditional guardian angels, a specific category of angelic beings said to be assigned to watch over each person. Despite functional similarities, these two categories of beings (ghosts and angels) have traditionally been regarded as entirely distinct. Today, however, because many people who have undergone near-death experiences have reported seeing deceased loved ones on 'the other side,' the distinction between disembodied helper spirits and guardian angels has blurred for many." (Angels A-Z pp. 373-374 by James R. Lewis and Evelyn Dorothy Oliver)
Indeed, many people believe in life after death and it is a sociological phenomenon across cultures and throughout historical time periods. Modern notions of guardian angels have no doubt adapted throughout history and across cultures. Paranormal psychology, in a sociological adaptation, can help explain why people believe in angels. Believing despite scientific or empirical evidence is truly remarkable, but very commons across cultures. I am going to think on this a little bit and try and formulate a meaningful thesis as to why people believe in angels.
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