The Vagaries of the English Language

Many and few.
You can say "many" and "few" (many are called but few are
chosen). You can say "a few" (a few of my favourite things) but you
can't say "a many" (unless you count "a many-splendoured thing").
On the other hand, you can say "many a" (many a new day) but you can't
say "few a".
What does it all mean?