Sentence:  Whenever New England liberalism is reminded of the dramatic confrontation of Parker and the fraternity on January 23 , 1843 - while it may defend the privilege of Chandler Robbins to demand that Parker leave the Association , while it may plead that Dr. N. L. Frothingham had every warrant for stating , `` The difference between Trinitarians and Unitarians is a difference in Christianity ; the difference between Mr. Parker and the Association <WSD>is</WSD> a difference between no Christianity and Christianity '' - despite these supposed conclusive assurances , the modern liberal heaves repeatedly a sigh of relief , of positive thanksgiving , that the Association never quite brought itself officially to expel Parker . 
Meaning of the word marked with <WSD> tags:  be identical to; be someone or something