I know very little about this, so if there are any Freeper's that would like to shed light on this subject I certainly would appreicate it. Thanks.
Opus Dei was not a project of Pope John Paul. It was started by Josemaria Escriva de Balaguer. The Pope Tolerated Opus Dei.
They wear spiked cilices and practice corporal mortification.
I think the reasoning for corporal mortification is, that we will all go to purgatory to pay for our sins. But while on earth we can pay for our sins here to make the path to heaven easier and faster when we die.