When we wish one another during the Aseres Yemei Teshuva "Gmar Chasima Tova" what does it mean? Does it not depend on what is written in the document? What difference does it make if the seal is good if the document is no good?
I'm sure others can give more in-depth answers but I believe this is the basic meaning: We say
בראש השנה יכתבון וביום צום כיפור יחתמון
Meaning, On Rosh Hashana our fate is written and on Yom Kippur our fate is sealed. Saying to someone "Gmar Chasima Tova" is simply wishing them that the fate that is sealed for them is a good one.
Until your fate is sealed, what is written can be changed. which is why the concluding service on Yom Kippur - Ne'ila is so important. That is the moment when what is written is sealed. Until that moment what is written can be changed for the better.
For more information check here look for the words "On Rosh Hashanah will be inscribed and on Yom Kippur will be sealed"
גמר חתימה טובה :)
Maybe it's because every Jew has a chezkas kashrus, so we assume he had a good writing.
Alternatively, you can change your writing during the Aseres Yemei Teshuvah, and even on Yom Kipur — otherwise, why would we still say in Avinu Malkeinu "כתבנו לחיים טובים," and similar things; and even בספר חיים ברכה ושלום נזכר ונכתב לפניך of the Shmoneh Esreh. (Of course, that would bring up the question of why we don't say לשנה טובה תכתב during these days as well, but maybe the first answer solves that.)
'Gmar Chatima Tova גמר חתימה טובה' is essentially wishing that someone being written (rosh hashana) and sealed (yom kippur) in the book of life. Gmar Chatima is an idiom for the sealing of the judgement, and tova, is that it should be a good judgement. You can also just say 'Gmar tov גמר טוב'
It literally means: may you be signed well (good). It is believd that in Yom Kippur a person's judgment is decided. Those who are lucky are written in the Book of Life and continue to live another year, and those have been too bad for too many years are written in the other book (which has no name, I think...)