。
Reading literature cultivates the mind.
Literal
Literature [object-を] read-[if-ば] mind [subject-が] is-nourished.
養われる is the passive of 養う (to nourish/cultivate). 心 here means 'mind' or 'heart/spirit.' The ~ば conditional gives a general-truth reading: 'if you read literature, the mind is nourished' — a universal statement.