He devotes himself to public service with the ideal of saving the world.
Tips
usage
Mostly used attributively or as a noun-modifier: 救世主 (saviour, the Christian Messiah), 救世军 (the Salvation Army), 救世情怀 (a saviour-mentality). Rarely used as a free-standing verb in modern conversation.
culture
In Chinese, 救世 sometimes carries an ironic edge — 救世主 can be used to mock self-appointed saviours: 别把自己当救世主 'don't treat yourself as the messiah'.