Larger Pureland Sutra

Thus the Tathagata takes pity on the threefold world with a great inexhaustible compassion. The Tathagata appears in the world in order to reveal the teaching of the Way everywhere, so that the multitude of living beings all reap the benefit of the true Dharma. Even in a myriad kalpas it is difficult to encounter and see the Tathagata. It is like the udumbara tree that blooms only after a long interval of time. But now that you have asked this question, numerous blessings will be bestowed on all living beings celestial and human. They will be guided and transformed.

From the Larger Pureland Sutra