Wherefore the Clapping of Hands?

Writing in the late 1900s, Lafcadio Hearn reports that templegoers in clap the hands thrice before praying to the Buddhist gods. Why three times?, he asks on a visit to a temple in Kamakura. His guide: once each for the Sansai, the three powers: Heaven, Earth, and Humankind. Hearn: Is the clapping meant to summon the gods? No, replies the student of the religion (the temple guide speaks English- Hearn himself never learned much Japanese)- it is to awaken oneself from the slumber that is existence, and from which prayer frees us. Apparently this practice of clapping has been discontinued since Hearn's day. https://www.kantsuji.tokyo/information/column/1592/