Martin Luther - a change of heart

From his letter to Fr. John Staupitz which accompanied the “95 Thesis”: (fourth paragaraph - click on the name to read the full letter)

“After this it came about that, by the grace of the learned men who dutifully teach us Greek and Hebrew, I learned that this word is in Greek metanoia and is derived from meta and noun, i.e., post and mentem, so that poenitentia or metanoia is a "coming to one's senses," and is a knowledge of one's own evil, gained after punishment has been accepted and error acknowledged; and this cannot possibly happen without a change in our heart and our love. All this answers so aptly to the theology of Paul, that nothing, at least in my judgment, can so aptly illustrate St. Paul.”