Keep in mind that it is only in the last 100 years that Christmas is perceived to be the most important Christian holiday. For most of Christianity’s history, Easter has been the most important annual celebration of Catholics, Orthodox and Protestants. This is because the crucifixion and resurrection of Our Lord is the whole purpose of Christianity.
That Mormons and JW’s don’t celebrate Easter speaks volumes.
Yes...altho technically for the earliest Christians over the first few centuries after Christ's death the most important day of recognition was Pascha -- Passover (where we get the word "Paschal Lamb" from)
There's a verse in Exodus where the Lord said He wanted this celebrated FOREVER... [no Old Testament/New Testament or Old Covenant/New Covenant distinction]
The blood of the Lamb -- the Paschal Lamb (Jesus) + His Resurrection is what changed the Sabbath from Saturday to Sunday.