Sentence:  So all-important <WSD>are</WSD> ideas , we are told , that persons successful in business and happy in social life usually fall into two classes : those who invent new ideas of their own , and those who borrow , beg , or steal from others . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)