I have a friend who introduced me to Joseph Campbell, who spent time studying myth and religion around the world, finding (in my understanding of his work) that they all shared many stories and pointed to the same thing.
I think this is an important issue. If we can find equivalents to nibbana, and the path to it in other religions, then our sources for information about the path are greatly multiplied. Or, as some do, we may decide that some subset of the Buddhist path is equivalent to the entire path itself and therefore we can narrow our focus to developing just a few traits.
My answer to this question is to ask the Buddha himself. I think the Buddha is no stranger to multiple points of view, metaphor, simile, and myth. In his time there seemed to be an explosion of various views/paths/beliefs. I'd like to limit myself to a few points that I think he makes emphatically:
: the idea that people can practice purification unrelated to their knowledge of the Buddha's specific teachings. This point is made in a teaching to Rahula: "Rahula, all those brahmans & contemplatives in the course of the past who purified their bodily actions, verbal actions, & mental actions, did it through repeated reflection on their bodily actions, verbal actions, & mental actions in just this way." (MN 61, http://www.accesstoinsight.org/tipitaka ... .than.html
" onclick="window.open(this.href);return false;) The Buddha then goes on to note that this is the case for present-day and future purifiers of mind and body. The emphasis is on the singularity of the path, explained to Rahula earlier as the development of the skillful and the abandonment of the unskillful. However I think that implicit in this formulation of the path is that it is universal and followed by Buddhists and non-Buddhists alike.
It seems that by this measure we should begin looking for nibbana in elements of Christianity and other religions, however this comparison has been done by the Buddha himself:
: given by the Buddha as a metaphor (or the explanation of the metaphor underlying) the Brahman practices of the time. Unfortunately I don't have a translation by Thanissaro Bhikkhu of the Subha Sutta, MN 99. Here is one from vipassana.info: http://www.vipassana.info/099-subha-e1.htm
" onclick="window.open(this.href);return false; . In this sutta the Buddha answers a quite combative interlocutor who tries to frame his teaching as being at odds with Brahmanism. The Buddha seems to think that the "two" paths have much in common:
‘Good Gotama, it’s good if I’m taught the path to be born in the world of Brahmaa.’
‘Then young man, listen carefully I will tell.’ The young man agreed and the Blessed One said.The bhikkhu pervades one direction with thoughts of loving kindness, so too the second, the third, the fourth, above, below, across, in every respect, in all circumstances, the entire world, he pervades with the thought of loving kindness grown great and immeasurable without anger and ill will. Young man, when the release of the mind in loving kindness, is developed thus, none of the measured actions remain. (* 1) Just as a clever drummer in no time would make known the message in the four directions. In the same manner, when the release of the mind in loving kindness, is developed thus, none of the measured actions remain. This is the method to be born with Brahmaa.. Again the bhikkhu pervades one direction with the thought of compassion,…re…. with intrinsic joy,…re… with equanimity, so too the second, the third, the fourth, above, below, across, in every respect, in all circumstances, the entire world, he pervades with equanimity grown great and immeasurable without anger and ill will. Young man, when the release of the mind in equanimity, is developed thus, none of the measured actions remain. (* 1) Just as a clever drummer in no time would make known the message in the four directions. In the same manner, when the release of the mind in equanimity is developed thus, none of the measured actions remain. This is the method to be born with Brahmaa..’
In other suttas the Buddha explains that this method does not only cause rebirth with Brahma, but brings one to these divine qualities in the here and now. It seems that the Brahmaviharas provide the link between Buddhism and religions that propose some unity with God. Of course the Buddha didn't know about Christianity and Islam, but my guess is that he would treat them in a similar way and find their ultimate expression in the cultivation of the brahmaviharas.
3) Brahmavihara is not Nibbana
: I think this theme occurs in many places, but here I give one support. In AN 9:16 we find:
“Monks, for one whose release of awareness through good will is cultivated, developed, pursued, given a means of transport, given a grounding, steadied, consolidated, and well-undertaken, eleven benefits can be expected. Which eleven?
“One sleeps easily, wakes easily, dreams no evil dreams. One is dear to human beings, dear to non-human beings. Devas protect one. Neither fire, poison, nor weapons can touch one. One’s mind gains concentration quickly. One’s complexion is bright. One dies unconfused and—if penetrating no higher—is headed for the Brahma worlds.”
Clearly here, and in many other places, nibbana is beyond the perfection of the brahmaviharas, which are tools to be used in development of the path.
My conclusion is that it's nice to make metaphorical links between religions, and I see this practice itself as an exercise of metta and good will. However, it seems that the Buddha did not believe that the path to nibbana was described in the religion of his time, and I doubt he would think that it is described in the various religions of our time. The logic is mine, but it is simple: The Dhamma is universal in some respects, yet most religion seems to be equivalent in the ideal to cultivation of the brahmaviharas, which the Buddha does not regard as nibanna nor the sole step in the path to nibbana.
On a personal level, I feel that the teachings of other religions head straight for the questions which the Buddha decided were unfit to be answered: "What am I?" "Who created the universe?" "What is the soul?"
In closing, I'm sure this passage is familiar:
"But then there is the case where a woman or man when visiting a priest or contemplative, asks: 'What is skillful, venerable sir? What is unskillful? What is blameworthy? What is blameless? What should be cultivated? What should not be cultivated? What, having been done by me, will be for my long-term harm & suffering? Or what, having been done by me, will be for my long-term welfare & happiness?' Through having adopted & carried out such actions, on the break-up of the body, after death, he/she reappears in a good destination... If instead he/she comes to the human state, then he/she is discerning wherever reborn. This is the way leading to discernment: when visiting a priest or contemplative, to ask: 'What is skillful?... Or what, having been done by me, will be for my long-term welfare & happiness?'" (http://www.accesstoinsight.org/tipitaka ... .than.html
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I think many of the religions fall short in answering these important questions in serious ways. They tend at best to fall second to the metaphysical questions that the Buddha avoids. I think in this sense the metaphor with other religions fails not only in the word of the Buddha, but also in the spirit of the Buddha's teachings.
Thank you for reading this long post. I'm glad there is a venue like this to post it to!