Translation:Easter is the biggest Christian holiday.
In the UK, christmas is bigger too but we are becoming less christian these days
Orthodox Christians hold that the resurrection of the living Christ is the most important day of the year. In Latin languages eg Spanish it is also called Pascua. Easter is the pagan name used by the germanic tribes for this time of year. Christmas is likewise not "Christ mass" but the Nativity (Navidad), ie the birth of Jesus the Messiah.
Answered "Easter is the largest Christian holiday;" would that be correct as well?
I would say no -- "big" can have the meaning "significant" but using "large" in this sense feels wrong to me.
It's rather annoying that in this module, "largest" and "biggest" are not accepted as synonyms. Third time now it was marked wrong for me.