You are astute to notice, because indeed "do penance" (corresponding to St. Jerome's "penitentia agite") suggests doing something, while "repent" suggests thinking something, but not necessarily doing anything as the outcome of the thinking. This therefore goes to the heart of our chief difference: we think that faith is something that we do; you think that faith is something that you think.
The expression, metanoete. comes from St. John the Baptist. And this is what we notice about St. John the Baptist: he was a doer. He gave an example of metanoia. What was that example? One followed by Christian monks everywhere: solitude; fast, hair shirt. He most certainly was doing penance rather than sitting in his office wispering to himself, "I think I am going to change my mind..."
