You guys should read Where the Heart Beats: John Cage, Zen Buddhism, and the Inner Life of Artists, which uses Cage’s biography and artistic exploration as a lead-in to general discussions on silence/meditation in the arts.
The original quote is from Cage's book A Year from Monday (page 44 here: https://monoskop.org/images/a/a3/Cage\_John\_A\_Year\_from\_Monday\_New\_Lectures\_and\_Writings.pdf), although I first came across it in Where the Heart Beats - John Cage, Zen Buddhism and the Inner Life of Artists by Kay Larson*,* possibly the best book on Cage ever written and the best book on his 'why':
Cage eventually revolted against Schoenberg's teaching, of course, although that isn't a bad thing - there is no question that Cage would have been long forgotten or would never have become the figure he was had he not done what he did. But Cage never revolted against Schoenberg the man, though. He had a lot of respect for him and always spoke highly of him.