Sentence:  Besides , it <WSD>'s</WSD> important to the way a painter thinks that he should move in a certain atmosphere , an atmosphere in which he may absorb the ideas of other masters , as Durer went to Italy to meet Bellini and Mantegna '' . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)