I'm particularly interested in if there is any evidence in the sutras (or commentaries or anything old) that explains this peculiar list of transgressions (the Ānantarika-karma):
- killing an arhat
- injuring a Buddha
- creating schism in the saṅgha.
1 & 2 & 3 are already against the first precept. 3 & 4 are hard to do even if you wanted to for lack of suitable arahats and Buddhas to kill or injure.
I've come to suspect that this is just a formula for expressing that schism is really bad. But this formula appears in many places, often without much other reference to schism. (for example ordination,