I grew up in the Seventh Day Adventist church culture and we would often have evangelistic meetings or what was called "Week of Prayer" with the stated goal of re-igniting the spiritual life. It was assumed that there was this God shaped hole in each person that needed to be filled, so the question, "Why do we need God?" was rhetorical in that context. Asking this question was a way to encourage an inward look at what might be lacking in a persons life.
It was assumed that no one would come to the conclusion that life was pretty good because, of course, humanity is fallen and under the curse of sin. And if this God shaped hole was empty this person was in need of salvation. So there was this sense of urgency and seriousness because lives were at stake and all problems would be solved once this hole was filled.
I would like to ask the question, "Why do we need God?" in a much different sense. Why do we need any type of god? What motivates humans to create all these different expressions of gods and goddesses?
In many forms of Christianity the world is portrayed as a great battlefield with a war being fought between Jesus and Satan for the souls of humankind. There is often fear that one might be influenced by Satan or even taken over. Making sure that Jesus is in one's heart is essential protection from the snares of Satan. There are many methods to make sure Jesus is in the heart including prayer and Bible study. The implication is if one leaves any part of the inner being unfilled by God or Jesus, it will leave an inroad for Satan to gain a foothold. One might make themselves more vulnerable by reading Harry Potter, using an Ouija board, doing Yoga, using meditation, magic 8 ball, or a host of other forbidden activities.
One of the major flaws I see in many religions is ultimately their core is based on fear, particularly the three Abrahamic religions of Judaism, Christianity, and Islam. Their world views all have some version of punishment and reward. And to deal with this fear one might make up all sorts of myths to make sense of the world.
I think we can recognize that we have a subconscious that filters a lot of sensory input and summarizes it for our conscious mind. The weakness of the conscious mind is that it can only pay attention to one thing at a time, while the subconscious processes things in parallel.
There is an interesting physical model of the universe being explored that sees the world as being holographic in nature. The unique property of a hologram is that it can be sliced in half and you still have the whole hologram. If this is true of reality then all the information that makes up reality is redundantly available locally for the conscious mind to access.
We simply can't process all that information at the same time, so the conscious mind passes this through our perception in a linear fashion so that we experience life as if time is passing.
One of the goals of many types of meditation is, not to check out, but to find a state where the chatter of fear stops and we can have our whole attention available to listen more closely and thereby become more conscious. This idea that the devil is just around every corner waiting to enter into our minds is simply another fear that can become a major distraction for some people.
There are a number of studies of people who master their art and professions. The thing they generally have in common is the ability to focus all their attention on their art for long periods of time.
This is why any belief system that focuses on fears tends to be self centered and reduces a person's ability to love and empathize. Fear also tends to keep a person immature.
In community, when people can really hear and see each other deep bonds form and life feels like it is meaningful. This provides the foundation for joy, our most sublime experience. Fear destroys all of this and most fears are based on illusions.
So if there is a Satan I would say it is simply fear.
It was pointed out to me that the Bible states perfect love casts out fear. To quote Tom Wetmore's answer, "That sort of confirms the framing of the great cosmic battle of God vs. Satan if God = love and perfect love casting out fear. In the end love wins. Fear loses the battle for the hearts and minds of the people."
This brings me back to the original question, "Why do we need god?" or "Why do we need to anthropomorphize the unknown?"
I think humans are afraid of the unknown so we tend to anthropomorphize these powerful influences on our experience. Love and fear are both powerful experiences that defy description because essentially they are both irrational.
I think Carl Jung describes this well as our tendency to draw on archetypes to help explain the great collective consciousness. Joseph Campbell does a great job of tracing these archetypes among different religions and traditions in his books on mythology.
I see nothing wrong with exploring spiritual experience using anthropomorphic representations of these mysteries. And I think that is why freedom of religion is essential for a healthy society. What crosses the line into harmful is when these representations are sustained as being real through force, coercion, and fear. When this is done I think it reveals a religion's immaturity and self centeredness of its members. It also removes the benefit that comes from the archetype by reducing the archetype into something less than human.
So when fear is the core motivation, the god that is worshiped is no longer a "higher power", but is something with even its humanity removed. Because, fear has no room for empathy.