Q: Why do we read the Passion on Palm Sunday and on Good Friday?
A: There’s evidence for proclaiming the Passion as far back as the third or fourth century. Prior to Vatican II all four Passion accounts were proclaimed during Holy Week – two of them on weekdays.
The Passion of John is always proclaimed on Good Friday. That is the most fitting day to hear one of the accounts. But the Church in wisdom knows that not everyone will attend the services on Good Friday. Hoping they’ll at least be there on the Sunday before Easter, the church gives us one of the other accounts that day. It’s mainly there for the people who won’t be back in church until Easter. It saves them from wondering, “What happened?”
You’ll find more in my book Glory in the Cross.