Tom Sawyer is Mark Twain's quintessential Romantic. Twain took almost every available opportunity to satirize Romanticism and its proponents in his works, and his creation of Tom is evidence of that. While readers love Tom for his vivid imagination, they should also note Twain's tongue-in-cheek portrayal of a Romantic (through Tom's character) as being too emotional, unrealistic, and impractical. Tom's attempt to recite Patrick Henry's speech in Chapter 21 is an example of what Twain saw as a Romantic's flaws. Tom, of course, has all intentions of delivering a stirring rendition of "Give Me Liberty of Give Me Death," but then
"a ghastly stage-fright seized him, his legs quaked under him and he was like to choke. . . . He struggled awhile and then retired, utterly defeated."
While Tom's failure on stage engenders laughter and sympathy from readers, it also serves to demonstrate from Twain's perspective that a typical Romantic has grand goals and visions but is often unable to carry them out when faced with reality.
From a more human perspective, Tom's stage fright makes him more human to readers. We should recognize that while he is an extremely savvy, entertaining character, he is still just a boy who reacts in a typically human fashion when faced with real (not imaginary) fears--such as public speaking.