What is the main reason behind this Mahayanist idea that The buddha gained enloightenment eons before Gautama time?

During the teaching it has been described that Buddha has become enlightened many eons before and what we saw as the historical Buddha was just a show to teach us the path to enlightenment. However, does it make difference that the Buddha attained enlightenment in this very life time? or in other words the historical Gautama just touched the selfless Buddhahood that has been there since the beginning-less time?

Gregory Hamilton Schmidt的头像

45 years is too short

I've also heard that a motivating factor is the relatively short career of the Buddha.

If in fact it took 3 innumerable eons to attain Buddhahood, 45 years seems like too short of a time for one to then reap the benefits for sentient beings.

I understand that even in the Khema Sutta, we are told that the Buddha is not known by his form, foreshadowing the explicit Mahayana position that the Buddha is not known by his marks, but by the Dharma.

The infinite capacity of the Dharma to rescue beings from suffering notwithstanding, this does seem to be a considerable incongruity.

The transcendental nature of the Buddha as outlined in the Lotus Sutra for example and the understanding of the parinirvana as skillful means at least addresses this perceived inconsistency.

4+5=9

I'd be VERY CAUTIOUS with taking such info from the lore literally.
4+5 (45)=9 the number of the great goddess, very popular in the counting of the yugas etc.
Gautama Buddha, too, practices asceticism with five companions – five like the fingers of a hand, the five senses, or the Upanishadic koshas that envelop the atman or soul- before enlightenment: the Buddhist response to either Vedantic philosophy, or the Mahabharata quest. Govind Singh (X and last Sikh guru ) chooses five men as first members of militant order Khalsa; each man is given the name of a virtue.
Regarding this matter of immemorial cycles spanning through eons separated by a flood or catastrophe, Campbell1 discusses numbers given in the lore according to ancient Hindu, Hebrew and Germanic sources that would allude to ongoing cycles timed according to Earth's precession of the equinox.

I can't reproduce Campbell's argument as it's too complex here. SOURCE:
Campbell, J., 1971/5, Tarot & Christian Myth, audio lecture, Joseph Campbell Foundation.

Campbell writes:

Let me take, as an illustration of the effect on mythology of this disenchanting
turn of mind, the example of the Deluge. According to many of the mythologies still
flourishing in the Orient, a world flood occurs inevitably at the termination of every aeon.
In India the number of years of an aeon, known as a Day of Brahma, is reckoned as
4,320,000,000; after which there follows a Night of Brahma, when all lies dissolved in
the cosmic sea for another 4,320,000,000 years, the sum total of years of an entire cosmic
round thus being 8,640,000,000. In the Icelandic eddas it is told that in Valhall there are
540 doors and that through each of these there will go at the end of the world 800 battleready
warriors to join combat with the anti-gods.4 But 800 times 540 is 432,000. So it
seems that there is a common mythological background theme, here shared by pagan
Europe with the ancient East. In fact, I note, with a glance at my watch, each hour with
60 minutes and each minute with 60 seconds, that in our present day of 24 hours there
will be 86,400 seconds; and in the course of this day, night will automatically follow
light, and, next morning, dawn follow darkness. There is no question of punishment or
guilt implied in a mythology of cosmic days and nights of this kind. Everything is
completely automatic and in the sweet nature of things.
But now, to press on a few steps further: according to a learned Chaldean priest,
Berossos, who rendered in the early third century B.C. an account of Babylonian
mythology, there elapsed 432,000 years between the crowning of the first Sumerian king
and the coining of the Deluge, and there reigned during this period ten very long-lived
kings. Then we observed that in the Bible it is reckoned that between the creation of
Adam and coming of Noah's Flood there elapsed 1656 years, during which there lived ten
very long-lived patriarchs. And if I may trust the finding of a distinguished Jewish
Assyriologist of the last century, Julius Oppert (1825-1906), the number of seven-day
weeks in 1656 years is 86,400.

FWIW

Another devise

In general, we can view every religious doctrine in two ways: based on a historical scientific approach, and based on an ahistorical faith-based one. Historically speaking, the Buddha was an ordinary man who went to homelessness in his search of the truth. The miracle of the Buddha was his deep insight which went beyond the appearances and could analyze the phenomena. To say that "the Buddha was an ordinary but genius man (ordinary in term of his metaphysical status)" will not undervalue what he did. Conversely, it will underline the importance of the Buddha's achievement. However, if we adopt a faith-based approach we can view the Buddha as a super mundane being ( I am not refuting the idea of a super mundane Buddha, I am just analyzing the two approach without accepting or rejecting them).
We can see the second approach in another way: the Buddha was an ordinary man, but what about "the essence" of enlightenment. I use the word essences in a casual manner because I cannot find a better word. If we view the issue in this way then we can say that "the Buddha was the emancipation of an primordial Buddha. Lets view the whole story of enlightenment eons before the historical Buddha appears", as another devise or skillful means to convey the message: the historical Buddha himself is not a god or something like that, the enlightenment itself is important.

archetype

Such developments are common to religious streams.
Some consider Jesus an enlightened Jewish preacher; others explicitly put him in the footsteps of Zoroaster (Arabic Infancy Gospel Of The Savior; incidentally, possibly the oldest indo-european religion still in existence); others yet in the footsteps of the Jewish rabbinical tradition as Yehoshua Ben Pandira, a disciple of noted rabbi Ben Perachia who started his ministry in 154 BCE. ). The majority consider him THE son of god and so on.
No wonder Gautama Buddha can either be an enlightened Indian ascetic, or the projection on the earthly plane of a quintessential Buddha in existence since time immemorial (cfr Della Santina's explanation). Buddha can either be a paradigm of an evolved human being, or a superhuman essence we can worship.
Avalokitesvara can be male, or female (Kwan Yin). KwanYin as a female was born pure and devoted to motherly love and compassion for all, which enraged her noble father. As a result, she had to endure trials and tribulations very similar to the Cinderella story. Kwan Yin barely escaped death as she was spirited away to a remote island as befallen to many heroines of Graeco-Roman myth. Furthermore -like Magdalene- Kwan Yin is often depicted with the vial of the dew of compassion, in turn reminiscent of Pandora and her box; and -like Mary- she is often depicted with an infant. Following other mythical heroes, she willingly sacrifices her bodily integrity1 to benefit her evil father (sparagmos=ritual dismemberment which befell countless deities from Orpheus to Bacchus, Romulus etc etc.

Those are archetypes that transcend cultures, space and time as they embody what people in all cultures have in common: the human psyche.

Two truths

Sammuti sacca can describe what was happened in North India 25 centuries ago.
Paramattha sacca can describe what is going on under Bodhi Tree now metaphorically speaking.
In my oppinion first of all Buddhism is like fruit which can be taste not as a science with a lots of nooks and crannies.