Today we celebrate Pentecost - the birth of the Catholic Church!
The Holy Ghost descends upon the Apostles on Pentecost - and as they "went out" and preached, starting with this day, the Lord added to the number of believers daily (Acts 2:47). St. Peter, our first pope, stood out as the leader and spokesman for the Church that first Christian celebration of Pentecost (Acts 2:14).
Pentecost also marks the end of Eastertide and begins the ordinal (counting, not "ordinary") days between Pentecost and the "New Year" of the Church - which is Advent.
If you have not made your "Easter Duty" by this time, all is not lost. Get yourself to Confession as soon as you can (you do not want to remain in mortal sin - separated from Saving Grace) and continue to observe the "Sunday Obligation" from here on out.
Godspeed, my friends.