Ambrose of Milan : 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. — On the Mysteries 3.14 Jerome : As wood sweetens Marah so that seventy palm trees are watered by its streams, so the cross makes the waters of the law lifegiving to the seventy who are Christ's apostles. — LETTER 69.6 Maximus of Turin : In this mystical number, I say, the children of Israel, arriving at Marah and being unable to draw the water because of its bitterness (for the well had water but no sweetness, and it was pleasing to the eye but polluted to the taste), drank water that became sweet and mild as soon as wood was thrown into it by Moses. The sacrament of the wood removed the harshness that the noxious water bore. I believe that this happened as a sign, for I think that the bitter water of Marah is the Old Testament law, which was harsh before it was tempered by the Lord's cross. — SERMON 67.4 Tertullian : Again, water is restored from its defect to its native grace of "sweetness" by the tree of Moses. That tree was Christ, restoring of himself the veins of what had been envenomed and bitter nature into the all-salutary waters of baptism. — ON BAPTISM 9.2