An invitation -- Repentance here means a change of heart -- A five-hundred-years-ago argument over penance -- Justification by faith versus the penance system -- Five hundred years of conflict -- Repentance calls for dialogue, dialogue focuses on repentance -- Ecumenists repent: the change of heart -- From mere diversity to reconciled diversity -- Reconciled diversity over justification -- Sacraments and practices among repentant Christians -- Can one day change the world? -- The ninety-five theses.