I don't know if it was a phase in time, or if it was a phase in just my life, but somewhere in the past (and in fact a little even now), there are/were those who would eschew the traditional 'Merry Christmas' for 'Blessed Christmas'.
Perhaps the word 'merry' was too much associated with the froth of commercialised Christmas, or else with the mad drunkenness that characterises the manner in which some celebrate the occasion.
'Blessed', on the other hand, carries with it connotations of divine presence, of the action of God. At the very least, something that is blessed has to be good as well. Hence the idea that a 'blessed' Christmas is perhaps more meaningful than a 'merry' one.
I don't know if such a point of view can be substantially defended, but this year, I feel exceptionally comfortable greeting others with a 'Merry Christmas!' and a lot less so with 'Blessed Christmas!'
Maybe it's because merriment sounds like joy overflowing, if we do not perpetuate its unfortunate association with drunkenness. And maybe also, merriment is a far more concrete emotion or state-of-being than 'blessedness'. For in a world where joy seems scarce these days, I can only imagine that Merriment either sounds like the echo of the greatest news ever heard, or else the most ridiculous story told by a drunkard.
And we are not all drunkards, certainly.
In the words of Uncle Scrooge's nephew, Fred; "Merry Christmas, Uncle! And a Happy New Year!"