swear by somebody

Từ điển Oxford Advanced Learner 8th

ˈswear by sb/sth derived
1. to name sb/sth to show that you are making a serious promise
•I swear by almighty God that I will tell the truth.
2. (not used in the progressive tenses)to be certain that sth is good or useful
•She swears by meditation as a way of relieving stress.
Main entry: ↑swear_derived