Sentence:  A century ago , Newman saw that liberalism ( what we now might call secularism ) would gradually but definitely make its mark on English Protestantism , and that even high Anglicanism would someday no longer <WSD>be</WSD> a `` serviceable breakwater against doctrinal errors more fundamental than its own '' . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)