The cross is the intersection where God meets humanity.  Saving confession is not predicated on prior knowledge, proximity to Jesus, or privilege; it is, rather, an act of faith in a divinely revealed act of atonement.

The centurion’s confession is the saving proclamation of the church, for it is the convergence point of Mark’s two major themes: the meaning of Jesus and the meaning of faith.

The Son of God, on whom rests the unique blessing and love of the Father, chooses not to exalt himself but to follow a path of servanthood, indeed of vicarious suffering and death, so that through the cross the world might acknowledge him to be the Son and with him share free and joyful access to the Father.

(James Edwards, The Gospel According to Mark, The Pillar New Testament Commentary, 2002, p. 483.)