Dieter Böhler, «Liebe und Freundschaft im Johannesevangelium. Zum alttestamentlichen Hintergrund von Joh 21,15-19», Vol. 96 (2015) 599-608
This article argues that Jesus' threefold question to Peter in John 21,15-17 is not the same question posed three times but, rather, three different questions of which only the last one gets a clear "Yes". Jesus asks Peter if by now he had reached that love which is ready to give one's life for a friend. In John 13,37 Peter had professed loudmouthed that he was ready. In John 21,15-17 he acknowledges that he is not ready yet.