able person; person of talent
A somewhat literary set phrase meaning a capable or talented individual. Not an everyday colloquial term; more likely to appear in formal writing or elevated speech.
He is expected to be a truly capable person.
有為 (ゆうい) means 'capable' or 'promising', and 材 (ざい) here means 'material' or 'talent'. The phrase literally means 'material of promise', i.e., a person with the qualities to achieve great things. The exact historical derivation is uncertain, but it follows classical Chinese-influenced phrasing.