Almost all churches and believers observe at least a tiny section of the Christian calendar (Christmas & Easter). While observing these “holy days” (i.e. holidays) is obviously not any kind of requirement, the purpose of observing certain sacred holidays is to latch on to a form of yearly rhythm, as well as to unite oneself to the larger body of Christ. Much like the Jewish feasts and holidays that Jesus himself embraced, much of the global body of Christ across a spectrum of denominations and churches have learned the value of embracing a rhythm of common calendar observance.
Today is Ascension Day. Forty days after Easter Sunday.