Question II: How great a sin schism is

I assert first that Schism is a most grave sin.

It is proved, because it wounds a great good of the Church, which is the most splendid unity of the mystical body of the Church; whence it seems the gravest among sins against one's neighbor, as Valencia says, puncto 1. Hence the holy Doctors gravely reprehend this scission. So Irenaeus lib. 4. cap. 34., Chrysostom homil. 11. ad Eph., Augustine Lib. 2. de Baptismo cont. Donat. cap. 6.

I assert second that heresy is graver by its object, since it is against divine truth; yet by its harm Schism is often the worse, as is clear, and has been clear, from experiences, as they note with St. Thomas, Tannerus disp. 2. quaest. 6. dub. 2. num. 17.