Charles Ellicott Commentary Exodus 15:25

"An he cried unto Jehovah; And Jehovah showed him a tree, and he cast it into the waters, and the waters were made sweet. There he made for them a statute and an ordinance, and there he proved them;" — Exodus 15:25 (ASV)

The Lord showed him a tree. —There are trees that have the power of sweetening bitter water, but none of them is currently found in the Sinaitic peninsula, and the Arabs are not currently acquainted with any means of making the bitter waters of Howarah and the neighbouring springs palatable. Perhaps in ancient times there were forms of vegetable life in the peninsula that do not now exist there. Moses would scarcely have been “shown a tree” unless the tree had some virtue of its own; but, on the other hand, the tree alone is scarcely to be credited with the entire effect.

As in so many other instances, God seems to have made use of nature, as far as nature could go, and then to have superadded His own omnipotent energy in order to produce the required effect. (Compare our blessed Lord’s method in working His miracles.)

He made for them a statute and an ordinance. — God took advantage of the occasion to draw a lesson from it. He promised that, as He had healed the waters, so, if the Israelites would from now on faithfully keep His commandments, He would “heal” them (Exodus 15:26), keeping them free from all the diseases of Egypt, and from the far greater evil involved in their own corrupted nature and infirmity.