What is the corporal mortification that Opus Dei does?

What is corporal mortification that Opus Dei suppostly do? Is it true and what benefits come from it? Where are the roots of this act?

Dear John,

Not only Opus Dei, but all Catholics perform corporal acts of mortification by fasting and abstaining from food and other forms of self denial. After all Jesus did say: “If any man would come after me, let him deny himself and take up his cross and follow me.” Mark 8:34

Fr. Vincent Serpa, O.P.

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