How can I make dates correspond to annual events for a calendar, such as "Dec. 25th always equals Christmas"?

I was given an Excel workbook with a schedule for our organization that people manually enter events for each day (one sheet per week), but I'd like to improve it and make it more automatic, if possible.

Like the title says, I'd like to be able to have certain days and dates correspond to certain events, like Christmas in the title, but also things like "The second Sunday in May = Mother's Day," or even Easter, which varies a lot every year.

Since this is so specific, I don't even know what to look up online, so I'm open to references and videos.

EDIT: It's for a Catholic organization, so basically every day has a different saint/event, which is why it's not so simple.