And he cried unto the LORD; and the LORD showed him a tree, which when he had cast it into the waters, the waters were made sweet: there he made for them a statute and an ordinance, and there he proved them,
All Commentaries on Exodus 15:25 Go To Exodus 15
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.