To influence a person is to give him one's own soul. He does not think his natural thoughts, or burn with his natural passions. His virtues are not real to him. His sins, if there are such things as sins, are borrowed. He becomes an echo of someone else's music, an actor of a part that has not been written for him.

Summary

This quote suggests that when someone is heavily influenced by another person, they lose their individuality. Their thoughts and emotions are no longer authentic, but rather borrowed from the person who has influenced them. Their virtues become superficial, and their faults are not genuine. They essentially become a mere reflection of someone else's beliefs and actions, like an actor playing a role without having any say in the script.