References – MN 30: The Shorter Simile of the Heartwood 
“Can you reflect about the meaning of ‘essence and conventions’ in Amaravati Chanting Book, p. 5?” Answered by Ajahn Pasanno. [Conventions ] // [Buddha images] [Teaching Dhamma] [Ceremony/ritual] [Liberation]
Sutta: MN 30: Cūḷasāropama Sutta.
Devotion and Ritual: Becoming the Buddha [2017], Session 3, Excerpt 13