Stunned by what he has witnessed, the centurion declares, “Truly this man was God’s Son!” (Mark 15:39). Impressed by the manner of Jesus’ death and the signs that attend it, the Roman centurion confesses of Jesus what he should only confess of the Roman emperor: Caesar is not the “son of God”; Jesus the crucified Messiah is. The mockery is now over.
In calling Jesus the Son of God, the centurion has switched his allegiance from Caesar, “son of God,” to Jesus, the real Son of God. The centurion now ascribes to Jesus what he had earlier ascribed to Caesar: Caesar is not divi filius (“son of God,” alluding to the Latin title of the great emperor Augustus). Jesus is.
Evans, C.A. & Wright, N.T. (2009). Jesus, the Final Days: What Really Happened [ebook]. Westminster John Knox Press, Louisville, Location 394