And he cried unto the LORD; and the LORD shewed him a tree, which when he had cast into the waters, the waters were made sweet: there he made for them a statute and an ordinance, and there he proved them, He cried unto the Lord - Moses was not only their leader, but also their mediator. Of prayer and dependence on the Almighty, the great mass of the Israelites appear to have had little knowledge at this time. Moses, therefore, had much to bear from their weakness, and the merciful Lord was long-suffering.
The Lord showed him a tree - What this tree was we know not: some think that the tree was extremely bitter itself, such as the quassia; and that God acted in this as he generally does, correcting contraries by contraries, which, among the ancient physicians, was a favourite maxim, Clavus clavo expellitur. The Targums of Jonathan and Jerusalem say that, when Moses prayed, "the Word of the Lord showed him the tree ארדפני ardiphney, on which he wrote the great and precious name of (Jehovah), and then threw it into the waters, and the waters thereby became sweet" But what the tree ardiphney was we are not informed.
Many suppose that this tree which healed the bitter waters was symbolical of the cross of our blessed Redeemer, that has been the means of healing infected nature, and through the virtue of which the evils and bitters of life are sweetened, and rendered subservient to the best interests of God's followers. Whatever may be in the metaphor, this is true in fact; and hence the greatest of apostles gloried in the cross of our Lord Jesus Christ, by which the world was crucified to him and he unto the world.
It appears that these waters were sweetened only for that occasion, as Dr. Shaw reports them to be still brackish, which appears to be occasioned by the abundance of natron which prevails in the surrounding soil. Thus we may infer that the natural cause of their bitterness or brackishness was permitted to resume its operations, when the occasion that rendered the change necessary had ceased to exist. Thus Christ simply changed that water into wine which was to be drawn out to be carried to the master of the feast; the rest of the water in the pots remaining as before. As the water of the Nile was so peculiarly excellent, to which they had been long accustomed, they could not easily put up with what was indifferent. See Clarke's note on Exodus 7:18.
There he made for them - Though it is probable that the Israelites are here intended, yet the word לו lo should not be translated for them, but to him, for these statutes were given to Moses that he might deliver them to the people.
There he proved them - נסהו nissahu, he proved Him. By this murmuring of the people he proved Moses, to see, speaking after the manner of men, whether he would be faithful, and, in the midst of the trials to which he was likely to be exposed, whether he would continue to trust in the Lord, and seek all his help from him.