Mahayana/"large vehicle" refers to a spaceship supercomputer which the monks had been building after discovering an ancient alphabet (Gematria) which translates the 9 billion names of god. "they believe the Universe was created in order to note all the names of God and once this naming is completed, God will bring the Universe to an end. Three centuries ago, the monks created an alphabet in which they calculated they could encode all the possible names of God, numbering about 9,000,000,000 ("nine billion") and each having no more than nine characters. Writing the names out by hand, as they had been doing, even after eliminating various nonsense combinations, would take another 15,000 years; the monks wish to use modern technology in order to finish this task more quickly.
They rent a computer capable of printing all the possible permutations, and they hire two Westerners to install and program the machine. The computer operators are skeptical but play along. After three months, as the job nears completion, they fear that the monks will blame the computer, and by extension its operators, when nothing happens. The Westerners delay the operation of the computer so that it will complete its final print run just after their scheduled departure. After their successful departure on ponies, they pause on the mountain path on their way back to the airfield, where a plane is waiting to take them back to civilization. Under a clear night sky they estimate that it must be just about the time that the monks are pasting the final printed names into their holy books. Then they notice that "overhead, without any fuss, the stars were going out."
At least, that's what Arthur C. Clarke thought:)