"You must not have the intention to harm others, and you must have the intention to guard against others."

This is a folk saying.

The general meaning is: you should not have bad thoughts of harming others, but you should also beware of others and be wary of others.

Usage:

Educate people to be more vigilant, not only not to hurt others, but also to be careful.

Source:

Hong Yingming·"Cai Gen Tan": "You must not have the intention of harming others, and you must have the intention of guarding against others; you would rather be deceived by others than go against their deceit. ”