Anne Bancroft compiled a book called The Pocket Buddha Reader, which includes the following quote (pp. 113-114):
Sakka asked the Buddha: “Do different religious teachers head for the same goal or practice the same disciplines or aspire to the same thing?”
“No, Sakka, they do not. And why? This world is made up of myriad different states of being, and people adhere to one or another of these states and become tenaciously possessive of them, saying, ‘This alone is true, everything else is false.’ It is like a territory that they believe is theirs. So all religious teachers do not teach the same goal or the same discipline, nor do they aspire to the same thing.”
“But if you find truth in any religion or philosophy, then accept that truth without prejudice.” —Digha Nikaya
The last line concerns me because it does not appear in the original source; it seems to have been added in by the author without justification. I would advise people to check this ‘popularized’ version of the quote from the Digha Nikaya 21 (aka the Sakka-pañha Sutta) against non-commercialized translations, such as the ones available at Access to Insight or Wikipitaka. In those more reliable sources, you will not find Buddha saying “accept truth from all religions and philosophies” or any words to that effect. Actually, quite the opposite! Here, Buddha unequivocally states that the world’s religions do not all teach the same thing.
Immediately after this, Buddha is asked whether priests and contemplatives of other religions have reached nirvana: “No, only those who are liberated by the destruction of craving are fully proficient, freed from the bonds, perfect in the holy life and have perfectly reached the goal.” Buddha says that the means for attaining liberation from delusions are not even taught outside of Buddhadharma. Buddha explained in the Brahmajala Sutta:
Bhikkus, there are countless philosophies, doctrines, and theories in this world. People criticize each other and argue endlessly over their theories. According to my investigation, there are sixty-two main theories which underlie the thousands of philosophies and religions current in our world. Looked at from the Way of Enlightenment and Emancipation, all sixty-two of these theories contain errors and create obstacles… A good fisherman places his net in the water and catches all the shrimp and fish he can. As he watches the creatures try to leap out of the net, he tells them, ‘No matter how high you jump, you will only land in the net again.’ He is correct. The thousands of beliefs flourishing at present can all be found in the net of these sixty-two theories. Bhikkus, don’t fall into that bewitching net. You will only waste time and lose your chance to practice the Way of Enlightenment. (Translated by Thich Nhat Hanh, Old Path, White Clouds, pp. 399-400)
Clearly, not all worldviews are created equal. In Friendly Letter (vv.61-62), Nagarjuna says that the wisdom of the middle way is not made known by any other religion: “Ask if they propound what passes beyond ‘is’ and ‘is not’. Thereby know that the ambrosia of the Buddhas’ teaching is called profound, an uncommon doctrine passing far beyond existence and non-existence.” Bodhichitta and emptiness of inherent existence have no counterpart in Christianity or any other faith. At best, Jesus’ self-sacrifice has an affinity with bodhichitta, but a slight resemblance is not enough to claim “same idea, different word.”
When asked, “Don’t all religions teach the same thing? Is it possible to unify them?” the Dalai Lama said:
People from different traditions should keep their own, rather than change. However, some Tibetan may prefer Islam, so he can follow it. Some Spanish prefer Buddhism; so follow it. But think about it carefully. Don’t do it for fashion. Some people start Christian, follow Islam, then Buddhism, then nothing.
In the United States I have seen people who embrace Buddhism and change their clothes! Like the New Age. They take something Hindu, something Buddhist, something, something… That is not healthy.
For individual practitioners, having one truth, one religion, is very important. Several truths, several religions, is contradictory.
I am Buddhist. Therefore, Buddhism is the only truth for me, the only religion. To my Christian friend, Christianity is the only truth, the only religion. To my Muslim friend, [Islam] is the only truth, the only religion. In the meantime, I respect and admire my Christian friend and my Muslim friend. If by unifying you mean mixing, that is impossible, useless.
Jesus does not lead you to nirvana, and Buddha does not lead you to God. Christianity teaches a creator God, but Buddha said only mind is the creator. Christianity teaches one life (and after that, the judgment), but Buddhism teaches past and future lives. Christianity teaches an immortal soul, but Buddhism teaches anatman (“no soul”). These are diametrically opposed, so how can we reconcile them without being unfaithful to one religion or the other, and without being untruthful to ourselves?