"Trust thyself: every heart vibrates to that iron string." The first part is easy enough, and like all good figurative language, you can get the sense of what the second bit means, even if you can't put it into words. But I will try to. The first instruction is to put faith in yourself: then your speech, what art you make, your beliefs, all need no external validation, for you have recognized their innate value. This done, your heart enlivens; is strengthened by that foundational trust. I see that subsequent vibration as representing the exercise of freedom: to be who you are, to speak what you must, and to see in yourself a person belonging amongst the ranks of all the people who have lived as you wish to, which might be what presupposes the conviction that all of life is for you, too.
Emersonian hogwash!