It means that only if you are upright can you be qualified to evaluate other people's moral character, behavior, etc. "Only by your own integrity can you measure others" is an idiom, which is intended to remind people to set themselves according to their own standards, and at the same time respect the differences of others and not to judge others at will. This sentence tells us to maintain a humble, tolerant and fair attitude towards others, and not to judge others easily, let alone impose your own standards on others.