I don’t know exactly why…but Passion Sunday is the beginning of Holy Week where we really focus in on Our Lord’s passion, in preparation for Easter.
Having the passion at the beginning of the week really sets the scene.
The Passion which is read on Good Friday (if I’m not mistaken) is John’s account - with the preceding Passion Sunday being one of the other evangelists, depending on the liturgical cycle. This way we get to hear all four accounts.
Also, Good Friday isn’t a Holyday of Obligation (or even a public holiday) in some countries, but you can still hear the account of the Passion by attending Mass the Sunday before Easter - I think something would really be missing if this was missed right before Easter.
Just a few of my own thoughts. There may be other reasons.
Peace
Vince
