A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
exo 15:1SONG OF MOSES. (Exo. 15:1-27)
Then sang Moses and the children of Israel--The scene of this thanksgiving song is supposed to have been at the landing place on the eastern shore of the Red Sea, at Ayoun Musa, "the fountains of Moses." They are situated somewhat farther northward along the shore than the opposite point from which the Israelites set out. But the line of the people would be extended during the passage, and one extremity of it would reach as far north as these fountains, which would supply them with water on landing. The time when it was sung is supposed to have been the morning after the passage. This song is, by some hundred years, the oldest poem in the world. There is a sublimity and beauty in the language that is unexampled. But its unrivalled superiority arises not solely from the splendor of the diction. Its poetical excellencies have often drawn forth the admiration of the best judges, while the character of the event commemorated, and its being prompted by divine inspiration, contribute to give it an interest and sublimity peculiar to itself.
I will sing unto the Lord, for he hath triumphed gloriously--Considering the state of servitude in which they had been born and bred, and the rude features of character which their subsequent history often displays, it cannot be supposed that the children of Israel generally were qualified to commit to memory or to appreciate the beauties of this inimitable song. But they might perfectly understand its pervading strain of sentiment; and, with the view of suitably improving the occasion, it was thought necessary that all, old and young, should join their united voices in the rehearsal of its words. As every individual had cause, so every individual gave utterance to his feelings of gratitude.
exo 15:20Miriam the prophetess--so called from her receiving divine revelations (Num 12:1; Mic 6:4), but in this instance principally from her being eminently skilled in music, and in this sense the word "prophecy" is sometimes used in Scripture (Ch1 25:1; Co1 11:5).
took a timbrel--or "tabret"--a musical instrument in the form of a hoop, edged round with rings or pieces of brass to make a jingling noise and covered over with tightened parchment like a drum. It was beat with the fingers, and corresponds to our tambourine.
all the women went out after her with timbrels and with dances--We shall understand this by attending to the modern customs of the East, where the dance--a slow, grave, and solemn gesture, generally accompanied with singing and the sound of the timbrel, is still led by the principal female of the company, the rest imitating her movements and repeating the words of the song as they drop from her lips.
exo 15:21Miriam answered them--"them" in the Hebrew is masculine, so that Moses probably led the men and Miriam the women--the two bands responding alternately, and singing the first verse as a chorus.
exo 15:22wilderness of Shur--comprehending all the western part of Arabia-PetrÃ&brvbr;a. The desert of Etham was a part of it, extending round the northern portion of the Red Sea, and a considerable distance along its eastern shore; whereas the "wilderness of Shur" (now Sudhr) was the designation of all the desert region of Arabia-PetrÃ&brvbr;a that lay next to Palestine.
exo 15:23when they came to Marah, they could not drink of the waters--Following the general route of all travellers southward, between the sea and the tableland of the Tih ("valley of wandering"), Marah is almost universally believed to be what is now called Howarah, in Wady Amarah, about thirty miles from the place where the Israelites landed on the eastern shore of the Red Sea--a distance quite sufficient for their march of three days. There is no other perennial spring in the intermediate space. The water still retains its ancient character, and has a bad name among the Arabs, who seldom allow their camels to partake of it.
exo 15:25the Lord showed him a tree, which when he had cast into the waters, the waters were made sweet--Some travellers have pronounced this to be the Elvah of the Arabs--a shrub in form and flower resembling our hawthorn; others, the berries of the Ghurkhud--a bush found growing around all brackish fountains. But neither of these shrubs are known by the natives to possess such natural virtues. It is far more likely that God miraculously endowed some tree with the property of purifying the bitter water--a tree employed as the medium, but the sweetening was not dependent upon the nature or quality of the tree, but the power of God (compare Joh 9:6). And hence the "statute and ordinance" that followed, which would have been singularly inopportune if no miracle had been wrought.
and there he proved them--God now brought the Israelites into circumstances which would put their faith and obedience to the test (compare Gen 22:1).
exo 15:27they came to Elim, where were twelve wells of water--supposed to be what is now called Wady-Ghurandel, the most extensive watercourse in the western desert--an oasis, adorned with a great variety of trees, among which the palm is still conspicuous, and fertilized by a copious stream. It is estimated to be a mile in breadth, but stretching out far to the northeast. After the weary travel through the desert, this must have appeared a most delightful encampment from its shade and verdure, as well as from its abundant supply of sweet water for the thirsty multitude. The palm is called "the tree of the desert," as its presence is always a sign of water. The palms in this spot are greatly increased in number, but the wells are diminished.