Spirituality is generally perceived as the non-physical, unseen aspects of life:

1. the quality or fact of being spiritual.
2. incorporeal or immaterial nature.
3. predominantly spiritual character as shown in thought, life, etc.; spiritual tendency or tone.
4. Often, spiritualities. property or revenue of the church or of an ecclesiastic in his or her official capacity.

[Origin: 1375–1425; late ME < ML spīrituālitās. See spiritual, -ity]

Another way of looking at it is as "the collective unknown" where man has no definitive means of measuring, analyzing or dealing with. Religions historically have been the stewards of man's spiritual welfare, because they spoke authoritatively, even if not necessarily factually, of these unknown, unseen places, beings, etcetera.

Because it is unknown, it is regarded as mystical. As soon as something is understood mysticism and spiritual aspects become removed from it. Folks fearing the plague would put magic squares made of silver on their doors or nearby, believing this would protect them. The science of plague infection by the fleas on rats was still unknown and so mysticism and spiritual pleas were the order of the day. One can find plague-era paintings illustrating the Saints pleas to Jesus to barter for mercy on man.

The world was flat only a few short centuries ago. And beyond the edge of seas were great serpents and a form of hell for those foolish enough to venture off the edges. Seamen have had many symbolic and susperstitious habits to protect them from the many dangers. The masthead dates back to barbaric times where either a sacrificial representation (a virgin girl) or a fearsome representation was depicted in order to sail safely and appease or frighten mystical forces. Today it seems ridiculous, but it was very serious stuff back then.

That is the way it will be with all the vast unknown infinite universe (or god if you prefer). Each new facet that gets shifted from the unknown column into the known will lose its spiritual or mystical association. ESP, telepathy and life after death, reincarnation and countless other things will someday lose spiritual associations and become understood in scientific parlance. And when this happens, religions will adapt, morph and will have known this all the time and move on to address things still unknown and therefore "spiritual".

Everyone has an innate understanding of their connection to something greater than themselves and realize they are but a tiny facet in the vastly larger diamond of life. When they are so inspired and aware they can convey some of this infinite wonder in art, music, poetry and writing as well as other venues. The human experience is still a selfish one - while the infinite universe operates as a complete whole, selflessly. Things that are selfless, we recognize as more noble and advanced and when we act selflessly we feel much better than when we act selfishly. We understand intuitively that we must live our lives in a manner that attempts to overcome and defeat selfish interests and replace them with more noble selfless actions. This is of course very difficult to do when all around us are voices clamoring of the glory and joy in material pursuits.

But the universe is patient. It transcends time and space and will awaits the infinite growth of each of its infinite facets.