15:1 sang Moses. This is the first recorded “song” in Scripture, and is probably the “song of Moses” referred to in Revelation 15:3, where Moses’ song is combined with the “song of the Lamb” at the glassy sea in the heavenly temple. The latter is the final “song” in the Bible, and the theme of both the first and last songs, is the ultimate fulfillment of God’s purpose in creation. This victorious song of Moses after crossing the sea actually seems to be reflected in a series of inscriptions on cliffs in the Sinai peninsula discovered in the nineteenth century, either made by some of the Israelites at the time or possibly by later Israelite pilgrims desiring to memorialize the great event.
15:8 congealed. That is, “coagulated,” like gelatin.
15:20 Miriam the prophetess. This is the first reference to Moses’ older sister since the time she watched him in the ark of bulrushes where his mother had hid him from Pharaoh when he was a baby (Exodus 2:4,7). This is also the only reference to Miriam as a prophetess.