Something was said last night during the announcements at Mass. Did you catch it?
"Mass times for the Solemnity of All Saints Day, a Holy Day of Obligation, will be at..."
I don't know about you, but I tend to zone out during announcements. And, if that's the case, you probably didn't catch that you need to, to the best of your ability, make it to Mass tomorrow.
"Mass on a Tuesday!?" you ask. "And by the way Sam, what the heck is a Holy Day of Obligation?"