Why do people need religious beliefs and ideas?
I have always found the esoteric traditions of religion more interesting than the exoteric ones. Within Christianity, there are the ideas of Celtic Christianity as well as the whole tradition of Gnosticism. The early Church was hostile towards Gnostic thinking but, nevertheless, it seems likely that a lot of Gnostic thinking did get incorporated into Christianity on some level, as the Gospel of St John and the Book of Revelation seem to be part of that tradition. There is even speculation that one of the founding fathers had some affinity with Gnostic thinking.
Of course, esoteric ideas have a whole history, as expressed in the Rosucrucian movement, alchemy and, more recently, as well as the ideas of Emmanuel Swedenborg and Rudolf Steiner. More recently, drawing upon the ideas of Eastern thinking, we have the whole movement of theosophy. I have been to a few meetings run by The Theosophical Society. One particular thing that I was impressed by within that organisation is the whole idea of recognizing the truth underlying all religions and creeds. Religion understood on that level makes more sense in some cases than just confining ideas to one viewpoint. The reason I say this is because many people adopt the religious beliefs which they are brought up with as children. That seems to make it all seem too relative and I am in favour of understanding the religious quest on a universal level of meeting the human need for understanding and truth.
The role of the devil in Christianity is interesting. Having been brought up as a Catholic, I had immense fear of the devil, sin and hell. This was the point at which psychology stepped into the picture for me. I found the ideas of Carl Jung extremely important. In particular, his book 'Answer to Job' looks at the whole problem of evil within Christianity, and the whole idea of the devil critically. Jung is controversial in his approach because he sees the idea of the image of God as a Trinity as inadequate and suggests that psychologically the idea of a quarternity is more consistent with the needs of the human psyche. The fourth aspect which he suggests is the the devil, and, or the feminine principle because he thinks that these have been repressed and suppressed within Christianity. In particular, he thinks that we need to become aware of our own dark side, the shadow, which if not faced cconsciously can result in evil being unleashed in a horrific way. Rather than seeing the devil outside of us, he sees it arising within us as destructiveness, especially in the possibility of nuclear devastation which could be carried out. Jung was writing this in the 1950s and I am sure that there are other threats, including terrorism.