“How rare, World Honored One, is the Tathagata who remembers and protects all Bodhisattvas and causes them to be well-endowed.”

The rare occurrence Subhūti refers to is the appearance of a Buddha, a World Honored One. Śākyamuni Buddha had arranged his seat and sat down without saying a word. Was Subhūti making something out of nothing, making waves where there was no wind, setting up wrong where there had not even been a right, placing a head on top of a head, adding a mark to a mark; was he just looking for trouble? If the Buddha had spoken a principle or made a sign it might have made sense to respond, “How rare, World Honored One,” but all Śākyamuni Buddha had done was arranged his seat and sat down.

This passage merits very special attention, for the main point of the Vajra Sutra is right here. By the time Śākyamuni Buddha had arranged his seat and sat down, he had already finished teaching dharma. That is why Subhūti uttered his words of praise. For Śākyamuni Buddha had taught the prajña of real mark, which is apart from the mark of the spoken word, apart from the mark of the written word, apart from the mark of the conditioned mind, apart from each and every mark. Only sages who had certified to the fruit understood; common people were not up to it. Realizing that, Subhūti hoped Śākyamuni Buddha would speak a provisional teaching, an expedient dharma of literary prajña, for the sake of living beings. That is why he prefaced his request for dharma by saying, “How rare is the World Honored One.” Truly rare is the Tathagata. Rarely is there a World Honored One. The real mark prajña is a protection and an endowment for all Bodhisattvas. The dharma is extremely wonderful.
The Vajra Prajna Paramita Sutra, p36-37