Moses purifies the waters (Exodus 15:22-27)

The story of Moses purifying the waters is included in the Book of Exodus. As a healing miracle involving wood and water, it was later understood to have hidden meanings.

After miraculously crossing the Red Sea, the Israelites travelled into the desert. For three days they searched for drinking water before arriving at Marah. Although there was water there, it was bitter and undrinkable. In their thirst, the people complained about it to Moses.

Moses then prayed to God, who showed him a particular tree and told him to throw it into the water. The water was then purified and made good to drink. Through this miracle, God reminded his people that he was their healer.

In keeping with this, the Book of Sirach refers to the story to prove that healthcare is a gift from God:  “Honor the physician, for he is essential to you; for that profession was established by the Lord…. The Lord has created medicines from the earth, and no one who is sensible will despise them. Was not water once sweetened by a tree so that his power might be revealed?” (38:1, 4-5)

Christian interpreters later connected the tree with the wood of the cross, and the purified water with the mystery of baptism. In the Middle Ages, the story was referred to in annual prayers to bless baptismal fonts.

This stained glass image of Moses throwing the wood into the water reflects this understanding. It’s found within the baptistery of St James Spanish Place, in London, alongside other water stories from the Bible, such as Noah’s Ark, Moses striking the rock, and the Temple in Ezekiel.

The window dates to 1925 and is the work of Geoffrey Webb, a Catholic artist whose stained glass studio was based in Suffolk. Moses is pictured with rays of light emerging from his head, which happened after he met God on Mount Sinai. He is throwing a log into the water rather than a tree – both interpretations of Exodus are possible.

Looking at the context, Exodus 15 is really a sequence of water stories. It describes the escape through the Red Sea, then the purifying of the waters of Marah, and finally the arrival at the oasis of Elim. At its centre stands Moses, whose very name means “drawn out of the water.” (Exodus 2:10)

Where to find this work of art
St James Spanish Place, London – baptistery only by arrangement

Read the relevant passage
Exodus 15:22-27

On a similar theme

• From the Old Testament: Moses worked other water miracles, such as parting the Red Sea and striking the rock.
• From the New Testament: Christ performed his own water miracles, including turning the water into wine and calming the storm.