Thank you for the opportunity to help you with your question!
the quote envy is ignorance... imitation is suicide from Emerson means that you must act naturally. For example Visionaries like Emerson trust that individuals need to comply with their own particular hearts as opposed to listening to what society instructs them to do. In this quote it means that it is moronic to need to be similar to other individuals. Attempting to copy other individuals is similar to murdering yourself. He is stating that you must be content with who you are. Thus, the significant thought here is that you must act naturally - you can't be what any other individual is or what any other person supposes you ought to be.
Please let me know if you need any clarification. I'm always happy to answer your questions.