Sentence:  I think it <WSD>is</WSD> essential , however , to pinpoint here the difference between the two concepts of sovereignty that went to war in 1861 - if only to see better how imperative is our need today to clarify completely our far worse confusion on this subject . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)