We often characterize the lives of human beings of the ancient past as filled with a profound sense of mystery. When saying this, many of us mean that ancient peoples were ignorant and susceptible to any idea suggested to them, a very unkind and irrational presumption. But if we mean to use this word "mystery" in its deepest, oldest sense, I believe it would be inaccurate to assume a sense of mystery in people long ago, simply because they seem to us so very mysterious. They were human, as we are, despite the differences in our external lives. They thought and felt, grew up and grew old, ate, drank, slept - only their methods were different. We have changed less in our interior lives from these ancient humans than many assume, I think. When we truly examine the history of the daily lives of people in those times, they were little different from our own, and daily life seemed to afford them as little a sense of mystery as it does in these modern times.
Mystery nowadays has been relegated to either an archaic form, almost exclusively used in religious thought (such as the Mysteries of the Rosary), or to denote something we know little about. While both senses are not entirely incorrect (the second incorrect only because of the ignorance most people have about its meaning), the original meaning of mystery was quite different. Rather than indicating our ignorance of a certain topic, mystery connoted an awareness of the invisible things of reality, within ourselves and outside. We are naturally capable and indeed drawn to seek the invisible. This is the primary impetus that inspires genuine spirituality, but many limit mystery only to direct experiences of the supernatural, or to a vague sense of awe at our ignorance about the world. In truth, mystery reflects a deeper awe at the essential ineffability of reality itself, even our very lives. It is a recognition of the dispersion of the invisible throughout reality, in all things. The very experience of life and being are mystical experiences.
Mysticism is very old. While in ancient religions, especially the Greek "mystery religions", spirituality was limited to a select view, it was opened to all with Christianity. Like its "mystery" root, Mysticism is the state of awe I described - the experience of awareness of the invisible, both positive and negative. Further, true Mysticism is an understanding of the root of all invisible things in the Divine, the Great Mystery. Beauty, truth, love, reason, life, death, consciousness - all these things are invisible, as are good and evil, revelation and deception, law and crime. Human beings alone are capable of recognizing the invisible. We have many different ways of understanding the invisible, particularly reason and the imagination, the former grasping truth and the latter, meaning. Both contribute to Mysticism.
As finite beings, we will always lack complete knowledge of anything. But this is not a bad quality - we are not made to become God, but to be like Him, non-Divine yet complete mirror images. Meaning is the evidence of will, of intent and purpose, while truth is the actual reality of a thing. Even without complete information or understanding, reason can judge the sensibility of something and judge it to be true - living according to these truths is faith. While truth is invisible, meaning is more ineffable to us - reality can exist as a principle of a thing itself, but all meaning derives from the Will, God Himself. Even human will cannot create meaning - we can only identify, receive and experience it. The experience of meaning is integral to Mysticism.
By recognizing the Divine Will of God in and above all things, even within the farthest depths of ourselves, we may live in a constant state of profound spirituality. Every moment in time becomes an experience of the sustaining Mind of God. Every thought becomes a transmission of the human soul, itself spirit and connected to the very Life of God. In this way, we may "pray unceasingly", as St. Paul instructs us, forever contemplating, living and breathing the infinite mystery of Being.