I pulled just a portion from this website: http://www.phrases.org.uk/meanings/merry-christmas.html ... as a good example ...
"The best-known allusion to merriment at Christmas is the English carol God Rest Ye Merry, Gentlemen. The source of this piece isn't known. It was first published in William Sandys' Christmas Carols Ancient and Modern in 1833, although versions of it probably existed as a folk-song and tune well before that but weren't written down. Sir Thomas Elyot, lists the phrase 'rest you merry' in his Dictionary in 1548: "Aye, bee thou gladde: or joyfull, as the vulgare people saie Reste you mery."
It is often assumed that the carol's lyric portrays the wish that jovial gentlemen might enjoy repose and tranquility. The punctuation of the song suggests otherwise though - it's 'God rest ye merry, gentlemen', not 'God rest ye, merry gentlemen'. In this context 'to rest' doesn't mean 'to repose' but rather 'to keep, or remain as you are' - like the 'rest' in 'rest assured'.
'Rest ye merry' means 'remain peacefully content' and the carol contains the wish that God should grant that favour to gentlemen (gentlewomen were presumably busy in the kitchen). It isn't the 'rest' that is being given but the 'merry'."
This is such a good example why I feel it is important for children to learn punctuation in written papers. Also, verbal dialogue can be misunderstood as well, especially in the age of "teleprompters" used by many, even the President! A good speech writer should know his punctuation and a good speaker should know the difference.
"Punctuation can accentuate the positive or negate the negative, totally changing the meaning of something."