Why did God prevent Herod from killing baby Jesus?
If we reduce the atonement to such a primitive, isolated transaction (as I believe PS does), there is no reason why the atonement would not “work” had Jesus died death by another means.
So why the cross? Why not just let Herod slaughter Jesus as a baby? If God just needed the death of someone who didn’t owe him death, than there’s no reason to stop the death of baby Jesus.
.. if God is unable to forgive us without a blood sacrifice to cover our sin, it once again makes no sense that Jesus freely forgave people on the basis of faith alone.