QUESTION: ”Buddhism is the belief that beings do get enlightened. Arhants and Buddhas do exist. "How can we truly know that? I don't know that I've ever met an Arhant or a Buddha. Am I even capable of knowing if I have?
SHORT ANSWER: Seeing is believing.
LONG ANSWER: The Buddhist movement began with and was spread by people who had met a Buddha called Shakyamuni. The whole tradition is a transmission of that particular charism. The truths taught be Buddhas are universal and are still true whether a Buddha appears to teach them or not, but the establishment of an actual tradition depends upon a Buddha appearing. Therefore, one evidence that a Buddha has appeared is the existence of this remarkable tradition that has transmitted the Dharma through 85 generations to the modern age.
When Dogen went to China he came back inspired because he had met a teacher who he thereafter referred to as an old Buddha. My own teacher, Kennett Roshi would say that when she went to Japan she saw some good practice and some awful practice, but along the way, “I met some real saints, and that is good enough for me.”
People are attracted to Buddhism primarily because they see there people who have something that inspires them, liberates them and encourages them. I know people who, because of their Western education, are highly skeptical of much Buddhist doctrine, who, yet, attend Buddhist events because they have met Buddhists who have something that they want - a happiness, inner strength and tranquility.
Faith, in Buddhism, does not stand opposed to experience. It stands upon a foundation of experience. Seeing is believing. The Buddha set out to create a cadre of people who would be a light. Their influence would bring peace, compassion and wisdom to the world. Of course, not every person who espouses Buddhism immediately lives up to this ideal. Nonetheless, I have met many great teachers and great souls. I did not agree with everything every one of them said, but I felt the quality of inspiration - the charism of Buddha - that flowed in their veins. It is that living faith that matters, not assent to intellectual propositions.
If I had not met Chogyam Trungpa, Kennett Roshi, Ato Rimpoche, Thich Nhat Hanh, Minh Chao, Saiko Sensei and others, then I would only know of Buddhism as an interesting theory in books. Buddhism is a living transmission. However, all of these great figures living the Noble Way in the midst of samsara are enlightened beings inasmuch as they are living the Dharmakaya. Their existence leads us to the unavoidable intuition of the Buddha as a property of this and all possible universes - the Cosmic Buddha, if you like. Each nirmanakaya great soul is different, has different character and different upaya because this is the conditioned world and we live here amidst diverse circumstances, but all are part of the same work. To worship one Buddha is to worship them all.
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