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Time is without beginning or end. There cannot be any point when time might have commenced and beyond which there was no time in the past. Similarly, there cannot be any point when the time would cease to exist and beyond which there would not be the future. So the time is without beginning or end. In other words, it is infinite. For our convenience, however, we can divide time into periods of short or long duration. Jainism divides time into time cycles of very long duration. During the first half of each time cycle, every thing goes on increasing and improving. That is the ascending part, which is known as Utsarpini. During the second half, every thing goes on declining and deteriorating. That is the descending part, which is known as Avasarpini.
Quite a number of souls attain omniscience and liberation from time to time. During every Utsarpini and every Avasarpini, however, there arise 24 Lords, who become outstanding, because they revive and reestablish the religious order during their time. Worldly souls have been undergoing the misery of births and deaths since the time immemorial. Well set religious order is helpful to them in crossing over that sea of recurring birth and death. Such order is therefore known as Tirth, which means 'helpful in crossing over'. Lords, who lay down such religious order are known as Tirthankars. At present, we are passing through a period of Avasarpini during which there have already been 24 Tirthankars. Lord Rushabhdev was the first and Lord Mahävir, who lived more than 2500 years ago, was the last.
To correctly comprehend the concept of Tirthankar, it would be helpful to know about certain vital aspects of Jainism.
Jainism has consistently believed in the following truths that science now admits:
i) Nothing can be produced out of nothing.
ii) What exists is going to exist forever in one form or another and every so called production happens to be merely a transformation of some thing that was existing earlier.
iii) The seemingly inanimate bodies like plants have life and they experience the sense of pleasure and pain.
Every living being is a combination of body and soul. Of these, the body is a tangible composition made of several substances and is bound to get decomposed. On the other hand, soul is intangible, shapeless and formless. It is an original substance that cannot be made by any composition and as such is not subject to decomposition. In other words, it stays forever. It has never been created. As such, the question of its creator does not arise.
There are innumerable visible and invisible species, in which the worldly soul has been taking birth after birth. This has been going on since the time immemorial. Presently, we are not able to know what was our previous life. But we can come to know of it by getting enlightened.