13 Faustus speaks of our God as astonished, which is not said in Scripture; nor does it follow that one must be astonished when he sees anything to be good. There are many good things which we see without being astonished, as if they were better than we expected; we merely approve of them as being what they ought to be. We can, however, give an instance of God being astonished, not from the Old Testament, which the Manichæans assail with undeserved reproach, but from the New Testament, which they profess to believe in order to entrap the unwary.
For they acknowledge Christ as God, and use this as a bait to entice Christ's followers into their snares. God, then, was astonished when Christ was astonished. For we read in the Gospel, that when Christ heard the faith of a certain centurion, He was astonished, and said to His disciples, "Verily I have not found so great faith, no, not in Israel." We have already given our explanation of the words, "God saw that it was good." Better men may give a better explanation. Meanwhile let the Manichæans explain Christ's being astonished at what He foresaw before it happened, and knew before He heard it.
For though seeing a thing to be good is quite different from being astonished at it, in this case there is some resemblance, for Jesus was astonished at the light of faith which He Himself had created in the heart of the centurion; for Jesus is the true light, which enlightens every man that comes into the world.
Source: Reply to Faustus the Manichaean (New Advent)