“Wait, Father Brench, my church is transferring All Saints’ Day to Sunday instead.”
Actually that’s not quite how it works. Our prayer book, on page 688, explains:
All Saints’ Day may also be observed on the Sunday following November 1, in addition to its observance on the fixed date.
Notice that this scheme gives us “two” All Saints’ Days. What’s really going on here is the last vestige of the ancient “Octave of All Saints.” We’ve discussed Octaves before, but it’s worth summarizing again: an octave is an eight-day period of time devoted to a special celebration. All the highest feasts of the year had one: Easter Octave (Sunday to Sunday), Pentecost Octave (Day of Pentecost through Trinity Sunday), All Saints’ Day (November 1st-8th), and I believe a few other holidays here and there also here. Modern prayer book tradition, with its allowance to celebrate All Saints’ Day on the Sunday within its octave, therefore preserves a piece of that ancient octave!
In short, if you’re celebrating All Saints’ Sunday, remember that today is still All Saints’ Day. The Daily Office lectionary has a special reading for this feast day in both Morning and Evening Prayer, which is exceedingly rare in the 2019 lectionary. So enjoy the holiday today, don’t fast, and sing For all the saints loudly on Sunday!