On what day did Jesus die and rise again?
In the Creed we say that “on the third day [Jesus] rose again,” but if Jesus died on a Friday and rose on a Sunday, isn’t that just two days?
In this video I explain the math behind the Resurrection and why St. Paul and even Jesus himself referenced the three days in the tomb between his death and Resurrection.
If the a day actually begins at sundown rather than midnight, it makes a lot more sense. Good Friday actually starts on Holy Thursday night. This is the first day during which Jesus died. Then, the second day begins in the evening on Good Friday continuing through Holy Saturday. The third day begins at sundown on Saturday night which is why we celebrate the Easter Vigil at that time.
These three days, of course, are the reason we celebrate the Paschal Triduum (or Easter Triduum) on Holy Thursday, Good Friday, and Holy Saturday.