Sentence:  Even if that 's all the promise he ever gave or ever will give , the giving of it once was enough and you believed it then and you will always believe it , even when it <WSD>is</WSD> finally the only thing in the world you have left to believe , and the whole world is telling you that one was a lie . 
Meaning of the word marked with <WSD> tags:  be identical to; be someone or something