When people come to see us, we foolishly prattle, lest we be inhospitable. But things said for conversation are chalk eggs. Don’t say things. What you are stands over you the while, and thunders so that I cannot hear what you say to the contrary.

Ralph Waldo Emerson (1803-1882) American essayist, lecturer, poet

“Social Aims,” lecture, Boston (1864-12-04), Letters and Social Aims (1875)
    (Source)

Likely source of the abridgments more commonly found *in:

• "What you do speaks so loudly that I cannot hear what you say."
• "What you are speaks so loudly that I cannot hear what you say."
• "Who you are speaks so loudly that I cannot hear what you say."
• "What we are speaks louder than what we say." [John F Kennedy, Q&A, Salt Lake City (23 Sep 1960), and in numerous subsequent speeches]

More discussion of this quotation: What You Do Speaks So Loudly that I Cannot Hear What You Say – Quote Investigator