A careful study of the spiritual development literature reveals that you most certainly do NOT have to believe in God to be spiritual. Various academic theorists who have studied this empirically, and some highly spiritual people writing about their own path, have all described a similar process by which a person comes into spiritual maturity. Taken together their writings can be lumped into a general category called spiritual development theory.
Though often cryptically worded, these writings show that the most spiritually mature among us may not believe in an actual literal God. That is, they may not believe that a bearded man up sits up in the sky, demanding we follow a bunch of sometimes muddled precepts and conflicting rules laid out in a holy document written thousands of years ago. They may not fear a heavenly creator sitting in judgment of our every move, hoping to grant us eternal reward in the afterlife or eternal punishment, depending whether we acknowledge him or not.
According to the spiritual development literature, those who have traveled the farthest on the spiritual development path have outgrown the need for this type of parent-figure God. Though they won’t tell you this in plain words, the “god” of the uppermost stages of the spiritual journey is more a metaphor than an actual being. It is certainly not the God of “popular” religion.
So if this is the case, why don’t they come right out and say so? One reason is the belief among those “in the know,” that knowledge about the spiritual stages is best kept from the general public. There is concern that without that judgmental God of fear and the threat of punishment, people will just go out and rampantly sin. As someone who has studied the literature carefully, I disagree. Many humanists, for example, are sufficiently self-governing that they don’t need fear and the threat of punishment to keep their behavior in line. Instead, many humanists are ruled more by principle than by rules. In fact, those not relying on pre-determined rules from a specific religion often have to think more deeply about what constitutes ethical behavior. They realize that circumstances may prevail where the more superficial rules may not suffice. In fact, in some cases a person without a religion is forced to develop a deeper sense of morality than one who simply follows the rules.
So what is meant by spirituality if it is not dependent upon belief in God? One definition of the word “spirit” involves a) “The vital principle or animating force within living beings.” And b) “incorporeal consciousness.” Well, we all have a) obviously. And b) is there whether we acknowledge it or not.
Have you ever just had a hunch something was going to happen, and it did? Have you ever felt something was just right for you to do and you went ahead with it and it turned out fine? Well, where did those notions come from? Not from your body. Not from the nerve cells and synapses in your brain, right? What is it that is looking out from your eyes? That is your spirit. The “incorporeal” part of your being. Everyone has this.
So what makes one person spiritual and another not? Rather than naïve belief in some improbably deity and the need for reassurance about what happens after bodily death, spirituality is about the ability to recognize the part of ourselves that is more than the sum of our cells. That we have something inside that keeps us from going out and just rampantly sinning when we don’t believe in a judgmental God of punishment. That “something” is our spirit – or spirituality. The more we can rely on that “something,” the more strongly developed it is, the more spiritual we are – regardless of what we believe about God. In their desperate hope to keep people from sinning, and their dire attempts to propagate the primacy of their belief system over others, the traditional religious institutions have robbed us of the one thing that unites all humans – our spirituality.
One thing that marks a more spiritual being is that he wants to access that which links him to others, like his general humanity and spirituality, not that which separates him, like strict literal beliefs.
What this means is, you don’t have to relinquish an important part of your humanity just because you can’t accept the literal stories about how you got here on earth and where you are going next. Those were written for people who need more security and certainty. Being able to give that up, in favor of the questions is another mark of spiritual maturity.
 Actually so far just about no one else calls it by that name. But having studied these works in great depth in preparation for my book, Faith Beyond Belief: Stories of Good People Who Left Their Church Behind, I found the correlations so compelling that I feel they must be condensed into a coherent theory.