The Buddha's teaching addresses something not immediately perceptible to us: our bondage to the Round of Rebirths.
From the selection of texts on similes regarding the boundless series of rebirths that has been cycling without any discernible beginning in time comes a frightening possibility.
This cycle is called samsara, a Pali/Sanskrit word that suggests the idea of directionless wandering or faring on. No matter how far back in time we may seek a beginning to the universe, there was never a moment of initial creation.
There are, however, periodic "creations" or, more correctly speaking, "impersonal formations" at the beginning of each world-system.
There was no creator; they simply follow a natural cyclical process of evolution and devolution. At times these world-systems are referred to as universes within a multiverse.
But if we reserve the term "universe" to everything in the entire cosmos inclusive of all the countless world-systems, there is no beginning to be found. World-systems last a great aeon (maha-kalpa) passing through four incalculable or uncertain phases: formation, duration, contraction, and an empty time.
This period of calm is followed by yet another formation, another revolution, which may be thought of as a Big Bang. But a Big Bang in no way explains the actual first cause or creation of the universe ("all that is") only another round of development, operation, chaotic dissolution, and quiescence.
Similarly, just as world-systems evolve and dissolve over billions of years, each different but each arising from the former, the same goes for individual rebirths. Each past and future life is a point along an ever-changing line of identity and attachment, the sense that a single entity is carrying on. Aggregates of clinging recur through countless deaths and rebirths.
As in the former case so in the latter, there is no beginning point to be found. Moreover, there would be no benefit to finding one if it became possible to find. For knowing it would not bring about the end of suffering (nirvana).
No matter how far back we may trace any given individual sequence of lives, we can never arrive at a first point.
How long will the Round of Rebirth last?
According to these texts (given in full In the Buddha’s Words: An Anthology of Discourses from the Pali Canon (Teachings of the Buddha), even if we were to trace the sequence of our mothers and fathers across world-systems, we would only come upon still more mothers and fathers stretching back into the far horizons.
Moreover, the frightening prospect is that the process is not only beginningless, it is also potentially endless! This may not seem frightful to anyone who does not see suffering -- or grasp the Four Noble Truths even intellectually -- and the potential for far greater suffering due to karma produced in ignorance driven by craving.
As long as ignorance and craving remain intact, the process will continue indefinitely into the future.
For the Buddha and Early Buddhism, this is above all the defining crisis at the heart of the our condition: We are bound to a chain of rebirths, and bound to it by nothing other than our own ignorance and craving.
The pointless wandering on in samsara -- suffering as we chase pleasure, enduring happiness, and security where it cannot be found -- occurs against a cosmic background of inconceivably vast dimensions.
The period of time that it takes for a world system to evolve, reach its phase of maximum expansion, then contract, and disintegrate is called a kappa (Sanskrit, kalpa) or aeon.
The texts offer vivid similes to suggest the duration of the various types of aeons; others offer vivid similes to illustrate the incalculable number of aeons through which we have already wandered interacting in all kinds of relationships with one another.
As beings fare along, wandering and roaming from life to life, shrouded in the darkness of ignorance over what is going on or what is causing the unsatifactoriness and rebirths, they fall again and again into the chasm of birth, aging, sickness, and death.
They fall again and again into the chasm of incomprehensibly woeful realms in the unfortunate destinations -- the worlds of animals, ghosts, monsters, and hellions.
Because their craving propels them forward in a relentless quest for gratification of sensual desires, ambitions, and running from pain, they seldom pause long enough to step back and carefully consider their existential plight.
Five Aggregates in the way a dog on a leash might run around a post or pillar. Since their ignorance prevents them from recognizing the vicious nature of their condition, they cannot discern even the tracks of a path to deliverance.
Most beings live immersed in the enjoyment of or the search for sensual pleasures. Others -- driven by the need for power, status, and esteem -- pass their lives in vain attempts to fill an unquenchable thirst.
Many, fearful of annihilation at death, construct belief systems that ascribe to their individual selves, their "souls," the prospect of eternal life. They do not perceive that this constructed "self" is perishing at every moment, changing, altering, and hurtling towards destruction.
A few yearn for a path to liberation. But they do not know where to find one. It was precisely to offer such a path that the Buddha has appeared in our midst. Buddhism originally was precisely a path-of-practice to the end of suffering.