All existing things pass through cycles that repeat. Everything passes through cycles of activity and repose, like the days and nights created by the rotation of our planet. Even the universe passes through cosmic days and nights. In Sanskrit, a cosmic day is a Manvantara. A cosmic night is called a Pralaya.
A Manvantara is a period within which there is activity of life, while a “Pralaya” is a repose of that activity. For instance, since you are alive, you are in a human-life “Manvantara.” When you die you will enter a “Pralaya.” The same happens for everything that exists, from the smallest particle up to an entire universe. Everything passes through days and nights, on small scales and great scales.
According to the Law of Seven that organizes all manifestation, seven Manvantaras (cosmic days) make one Mahamanvantara, a “great cosmic day” (maha means “great”). One great cosmic day is equivalent to 311,040,000,000,000 human years. Seven cosmic nights (pralayas) make one great cosmic night, a Mahapralaya. Life unfolds in series of sevens.
Like the seasons or the days and nights of nature, every Manvantara is both a recapitulation of past Manvantaras and an example of future Manvantaras. Today repeats many elements from yesterday, but with slight changes, which in turn predicts tomorrow. Thus, by careful awareness of these cycles, we can draw great knowledge about the past and future.
From H.P. Blavatsky:
“The Days of Nights of Brahma. This is the name given to the Periods called Manvantara (Manuantara, or between the Manus) and Pralaya (Dissolution); one referring to the active periods of the Universe, the other to its times of relative and complete rest -- according to whether they occur at the end of a ‘Day,’ or an ‘Age’ (a life) of Brahma. These periods, which follow each other in regular succession, are also called Kalpas, small and great, the minor and the Maha Kalpa; though, properly speaking, the Maha Kalpa is never a ‘day,’ but a whole life or age of Brahma, for it is said in the Brahma Vaivarta: ‘Chronologers compute a Kalpa by the Life of Brahma; minor Kalpas, as Samvarta and the rest, are numerous.’ In sober truth they are infinite; as they have never had a commencement, i.e., there never was a first Kalpa, nor will there ever be a last one, in Eternity.”
“Occultism divides the periods of Rest (Pralaya) into several kinds; there is the individual pralaya of each Globe, as humanity and life pass on to the next; seven minor Pralayas in each Round; the planetary Pralaya, when seven Rounds are completed; the Solar Pralaya, when the whole system is at an end; and finally the Universal Maha -- or Brahma -- Pralaya at the close of the ‘Age of Brahma.’ These are the three chief pralayas or ‘destruction periods.’ There are many other minor ones, but with these we are not concerned at present.”
Related to the planet Earth, we are presently in the midst of the Fourth Round. Our current humanity is the Fifth Root Race (of seven) to exist in this current Fourth Round, also called the “Terrestrial Round.” Previous to this round, there were three great rounds or cosmic ages:
As these rounds or cosmic ages have passed like days and nights on the universal scale, they have also brought a gradual change or evolution of matter and energy. Matter and energy have slowly condensed. At the beginning of the Mahamanvantara, when matter and energy first emerged, they were subtle, not physical. Over ages they have condensed to the physical level.
In the Saturnian Round, everything was very subtle, having only reached from the unmanifested (Atziluth) to mental aspect (Netzach) of the fifth dimension. After seven manvantaras, the universe then went into repose.
During the Solar Round, through gradual complication of cause and effect for millennia, matter and energy condensed to the astral aspect (Hod) of the fifth dimension. After seven manvantaras, the universe again went into repose.
During the Lunar Round, matter and energy gradually condense into the ethereal aspect of the fourth dimension (Yesod). This is the famous Eden of the Bible. Again, after seven manvantaras or cosmic days, the universe entered into repose.
Finally, all of that complication of matter and energy caused the Terrestrial Round to emerge, in which matter and energy condensed into the third dimension (Malkuth). We are the fifth human race of this current round. Previous to our current humanity, there were four humanities about which we are completely ignorant, aside from the humanities that existed in the other cosmic rounds.
Very soon, our manvantara will end, and a period of repose will occur, after which a new humanity will be born, continuing the eternal cycle of life, bringing the karma (cause and effect) of all the previous rounds, and adding their own.
All of this is visible in the development of the human fetus: the stages the fetus passes through as it grows into a human being are recapitulative reflections of all the previous human races, which over millennia gradually condensed from amorphous semi-physical and fluidic forms to the physical form we have today.
Thus does life flow: in cycles, series, like a great spiral that never ends.