Do you know which was the first feast day celebrated in the early Christian Church? Christmas comes to mind right away, though I am not sure if that is because I have logical reasons why I think it should be first or rather because it is my favorite feast day of the year. The answer is actually Easter, the Lord's resurrection. Reflecting for a moment, I have to say that it makes perfect sense. Everything else would have been pointless without the resurrection- it is what gave Jesus Christ not only credibility, but supremacy. He is the savior! No one else has conquered death. St. Paul wrote: "if Christ has not been raised, then our preaching is in vain and your faith is in vain." (1 Cor 15:14)
What do you think the next feasts to be added to the liturgical calendar? Sorry, still not Christmas. The second and third celebrations for which we have evidence are the feasts of the Ascension (Acts 1:6-11) and Pentecost (Acts 2- see picture above for how they celebrate Pentecost at the Pantheon!). At first glance, I would say that Christmas is more important than these feasts. The logic, though, is that these two feasts complete the celebration of Easter, the paschal mystery. Jesus said that he would leave us, but he promised that, after his resurrection, he would send us his Spirit. Pentecost marks the conclusion of the celebration of Easter-tide.
After these feasts, they also added feast days marking the days of the Lord's passion- Holy Thursday and Good Friday, along with Palm Sunday. The picture here may not look familiar, but it is the crucifixion. As a matter of fact, it is one of the earliest depictions of the crucifixion we are aware of as it may date to as early as the 5th century. It is on the large wooden doors of the Church of Santa Sabina here in Rome.
When we learned about this progression recently in Liturgy class, it really struck me because while the other feasts are truly important and significant, the celebration of Easter is the single, most significant feast in Christianity. Really, it is definitive and indicative of what sets Christianity apart. It is not so surprising, then, that this fact is witnessed even in the historical development of Christian worship.