They are the reason we are here, they are what matter most to all of us and it is gratifying to see so many of you giving your time and enthusiasm to make the day a success.
Curmudgeon, why wouldn't there be a comma before the coordinate conjunction "and" that preceeds "it"?
-- Rob
Good catch. Actually, the first comma is a bit of a problem also:
They are the reason we are here; they are what matter most to all of us, and it is gratifying to see so many of you giving your time and enthusiasm to make the day a success.
or
They are the reason we are here; they are what matter most to all of us. And, it is gratifying to see so many of you giving your time and enthusiasm to make the day a success.