Complex sentence: Therefore, since Dominguez's claim to the papacy rests on Private Revelation, his claim is non-binding, which would be absurd since Catholics believe that being subject to the Roman Pontiff is necessary for salvation.
Split into simpler sentences: Therefore, since Dominguez's claim to the papacy rests on Private Revelation, his claim would be non-binding. This would be absurd, since Roman Catholics believe that being subject to the Roman Pontiff is necessary for salvation.