鉴往知来

jiàn wǎng zhī lái

to observe the past to foresee the future (idiom, taken loosely from Book of Songs); studying ancient wisdom gives insight into what is to come

鉴

jiàn

bronze mirror (used in ancient times)

往

wǎng

to go (in a direction)

知

zhī

to know

来

lái

to come