Complex sentence: Historically, Shakyamuni was reactionary to the revealed authority of the Vedas the incantations and sounds of which were permanent and the sound and sign of the syllable or visible mantra was held to be non-other than what it communicated.
Split into simpler sentences: Historically, Shakyamuni was reactionary to the status of the revealed authority of the Vedas the ritual incantations and sounds of which were permanent. In the Vedic system, the sound and sign of the syllable or visible mantra was held to be none-other than what it communicated.