"Marah was a fountain of most bitter water: Moses cast wood into it and it became sweet. For water without the preaching of the Cross of the Lord is of no avail for future salvation, but, after it has been consecrated by the mystery of the saving cross, it is made suitable for the use of the spiritual laver and of the cup of salvation. As then, Moses, that is, the prophet, cast wood into that fountain, so, too, the priest utters over this font the proclamation of the Lord's cross, and the water is made sweet for the purpose of grace. 15. You must not trust, then, wholly to your bodily eyes; that which is not seen is more really seen, for the object of sight is temporal, but that other eternal, which is not apprehended by the eye, but is discerned by the mind and spirit."

The quote is beautiful in and of itself. But I also like the way that church practice / tradition is seamlessly interwoven with Biblical interpretation. While the fundamentalist would reject consecration of water for baptism and the mixed eucharistic cup because it lacks biblical precedent; the church of Milan in the late 4th century would never dream of doing it another way. (A practice that continues even today in Rome and the East.) The Fathers, as is obvious from the quote, read Scripture with a clear eye, and see the evidence of church faith and practice throughout.