"Christ, the Savior, has given Israel conversion and forgiveness of sins (v. 31) - in the Greek text the term is metanoia - he has given penance and forgiveness of sins."This for me is a very important observation: penance is a grace. There is a tendency in exegesis that says: Jesus in Galilee had announced a grace without condition, absolutely unconditional, therefore also without penance, grace as such, without human preconditions. But this is a false interpretation of grace.
"Penance is grace; it is a grace that we recognize our sin, it is a grace that we know we need renewal, change, a transformation of our being. Penance, being able to do penance, is the gift of grace. And I must say that we Christians, even in recent times, have often avoided the word penance, it has seemed too harsh to us. Now, under the attacks of the world that speak to us of our sins, we see that being able to do penance is grace. And we see that it is necessary to do penance, that is, to recognize what is wrong in our life, open ourselves to forgiveness, prepare ourselves for forgiveness, allow ourselves to be transformed.
"The suffering of penance, of purification, of transformation, this suffering is grace, because it is renewal, it is the work of divine mercy. And so these two things that Saint Peter says - penance and forgiveness - correspond to the beginning of the preaching of Jesus: metanoeite, which means be converted (cf. Mk. 1:15). So this is the fundamental point: metanoia is not a private thing, which would seem to be replaced by grace, but metanoia is the arrival of the grace that transforms us."
Full text at "For This Pope, All Is Grace, Even 'The World's Attacks on Our Sins' "
