Sentence:  A second rescript followed, commanding all bishops not merely to subscribe to the dominant opinions on these profound and <WSD>abstruse</WSD> topics, but to condemn their authors, Pelagius and Cœlestius, as irreclaimable heretics, and this under pain of deprivation and banishment. 
Meaning of the word marked with <WSD> tags:  Difficult to comprehend or understand. (First attested in the late 16th century.)<ref name=SOED/>