And he cried unto the Lord; and the Lord shewed him a tree, &c.— As soon as the Israelites felt the least inconvenience, they shewed that murmuring and discontented disposition, which so strongly marks their character. Their murmurs against Moses, Exodus 15:24 were, in reality, murmurs against GOD. Moses, however, was more wise; and, in fervent prayer, applied to Jehovah, who alone can help in the hour of distress. The Lord heard his prayer, and pointed out to him a particular tree, which was probably of such natural efficacy, as to produce the end desired; sweetening these bitter waters. It is, I believe, impossible to tell of what species this tree was; and therefore conjectures are vain. Pliny (lib. xiv. c. 2.) and other naturalists inform us, that there is wood which will work this effect: the miracle, therefore, probably, consisted in Jehovah's pointing out to Moses this particular species of wood. In this view the author of Ecclesiasticus considers it: Was not the water, says he, made sweet with wood, that the virtue thereof might be known? ch. Exodus 38:5. See 2 Kings 2:21-22; 2 Kings 4:41. Demetrius, a heathen writer, quoted by Eusebius, (Praep. Evan. lib. ix. c. 29.) reports this fact in the same manner as Moses. Some are of opinion, that Jehovah sweetened these waters by his own immediate power; and that the tree, or wood, which was cast into them, was only an external sign, and not the means of the miracle which was wrought on this occasion. See Shuckford's Connection, vol. iii. p. 7. The fathers have made some ingenious comparisons between this wood and the cross of Christ. See Parker's Bibliothec. &c. on the place.
There he made—a statute and an ordinance, &c.— It seems most natural to understand these words as addressed by Jehovah to Moses; for, he proved them, should certainly be rendered, he proved him, agreeably to the next verse: and Moses may be considered here, as the representative of all the people. See ch. Exodus 16:28-29. The Lord having proved or tried him, by this circumstance of the tree, and having found him faithful, here lays it down, as his fixed statute and determined ordinance, that if he, and the people committed to his charge, would continue faithful to his commands, he would deliver them from every evil disease and every calamity; and preserve them in health, as he was well able to do, being the Lord of health: for I am the Lord, that gives thee health; alluding to that health or sweetness, which he had just given, by his Divine interposition, to the bitter waters. The health of the Israelites was so remarkable at this time, that the Psalmist tells us, there was not one feeble person among them, Psalms 105:37. Junius translates this, I am God thy Saviour. See Jeremiah 7:22-23. I spake not unto your fathers, nor commanded them in the day that I brought them out of the land of Egypt, concerning burnt-offerings or sacrifices: but this thing commanded I them, saying, Obey my voice, and I will be your God, and ye shall be my people; and walk ye in all the ways that I have commanded you, that it may be well unto you: a passage, which would induce one to believe, that this was the original statute and ordinance, which GOD designed for his people; and that, had they been less discontented and refractory, they would not have been loaded with so burdensome a yoke of ceremonies: indeed we are told that this was laid upon them for the hardness of their hearts. Houbigant translates this verse, Moses prayed unto the Lord, who shewed him a tree; which being cast into the water, the water was made sweet. And there, after he had proved him, he made with him the following covenant, that it might be observed: Exodus 15:26. If thou wilt, &c. See ch. Exodus 16:4.