Sentence:  Again , Henley 's attitude of defiance which colors his ideal of self mastery is far from characteristic of a Stoic thinker like Marcus Aurelius , whose gentle acquiescence <WSD>is</WSD> almost Christian , comparable to the patience expressed in Milton 's sonnet on his own blindness . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)