5 Hear what is even more wonderful, that the hidden and veiled mysteries of the ancient books are in some degree revealed by the ancient books. For Micah the prophet speaks thus. According to the days of your coming out of Egypt will I show unto him marvellous things, etc....In this Psalm, therefore, although the wonderful spirit of prophecy does look into the future, yet it seems, as it were, to be merely detailing to the past. “Judah,” he says, “was His sanctuary: the sea saw that and fled:” “was,” “saw,” and “fled,” are words of the past tense; and “Jordan was driven back, and the mountains skipped, and the earth trembled,” in like manner have a past expression, without, however, any difficulty in understanding by them the future....For though it was so long after the departure of that people from Egypt, and so long before these seasons of the Church, that he sang what I have quoted; nevertheless, he witnesses that he is foretelling the future without any question.
“According to the days,” he says, “of your coming out of the land of Egypt will I show unto him marvellous things.” “The nations shall see and be confounded.” This is what is here said, “The sea saw that, and fled:” for if in this passage, through words of the past tense the future is secretly revealed, as is the case; who would venture to explain the words, “shall see and be confounded,” of past events? And a little lower down he alludes more clearly than light itself to those very enemies of ours, who followed us flying, that they might slay us, that is, our sins, which are overwhelmed and extinguished in Baptism, just as the Egyptians were drowned in the sea, saying, since “He retains not His anger for ever, because He is of good will and merciful, He will turn again, He will have compassion upon us, He will drown our iniquities: and You will cast all their sins into the depths of the sea.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)