In one of the few Markan narratives that John also tells, John, like Mark, has Jesus saying, “It is I” (i.e., “I am” [εγώ ειμι]; Mark 6:50; John 6:20). In John this becomes the second of the Gospel's theologically potent series of seven absolute “I am” sayings (4:26; 6:20; 8:24, 28, 58; 13:19; 18:5, 6, 8). For readers/hearers of Mark, this series would not only develop the christological significance of the “I am” sayings they already knew in Mark 6:50 but also inform their understanding of the “I am” saying in Mark 14:62. In ways such as this, it would be possible to argue that John provides readers/hearers who already know Mark with a much fuller and more developed christological and soteriological interpretation of the Gospel story, but one which had clear continuity with the Markan Christology and soteriology they already knew. They would not perceive John's interpretation of Jesus as correcting or invalidating Mark's, but as extending and deepening it. … With the benefit of John's explicit interpretations of the few “signs” of the Jesus which he has carefully chosen for his highly selective Gospel narrative, they could also read with fresh perception the “many other signs” (John 20:30) that Mark records. While the fourth evangelist surely meant to lead his readers further and deeper into the significance of Jesus and his story than Mark's Gospel had done, he need not have intended them henceforth to leave Mark aside and to read only his own Gospel. He did not aim to replace Mark, but to write a different kind of Gospel: one which, by selecting far fewer traditions, left space for the reflective interpretation that is the distinctive characteristic of the Fourth Gospel. [*]That, quite simply, rocks!
[*] R. Bauckham, “John for Readers of Mark,” in The Gospel for all Christians: Rethinking the Gospel Audiences (ed. Richard Bauckham; Grand Rapids: Eerdmanns, 1998), 169-170; cited in Seitz, Prophecy, 180-181