The great themes of the Pilgrimage Festivals in Judaism—Passover: Freedom/ Shavuot: the Law/ Succot: Thanksgiving for the Harvest—already have their secular counterparts.
What about the Christian holy days of Christmas and Easter? For a very long time, they will remain part of
As America becomes even more religiously pluralistic than it is now, the holy days of other religions will be added to the national calendar. Secularism, of course, will borrow these other themes as well.