There are many parallels in the Revelation found in the Old Testament (OT). The Song of Moses and the Song of the Lamb (cf. Ex. 15 and Rev. 15:1-3) is one of the most striking examples.
Although the Book of Revelation does not quote the OT verbatim, it alludes to it over 550 times*. What we find in Rev. 15, is the Apostle John alluding to the post-Exodus song celebrating the Lord's victory over Pharaoh, the enemy of God (Ex. 15). The title, "Song of Moses", is somewhat deceptive, because nowhere is Moses' name found in the Song. It was all about Jehovah's victory. Specifically, it was God Messenger (Angel) that protected them, the pre-incarnate Christ (Ex 13:21-22). In the same chapter we find Moses' sister, Miriam, breaking out in dance.
20.And Miriam the prophetess, the sister of Aaron, took a timbrel in her hand; and all the women went out after her with timbrels and with
21.And Miriam answered them, Sing ye to the Lord, for he hath triumphed gloriously; the horse and his rider hath he thrown into the
sea. (Ex. 15:20-21 KJV)
The OT prophet Isaiah wrote of another exodus that would take place when the Messiah would reign**. Most of what is called the Exodus Motif is found in Isaiah Chapters 40-55. OT Jews did not believe they would literally enter Egypt again to re-exit. In fact, the exiled Jews most likely understood their next exodus as a departure from the Babylonian captivity, yet there were future prophetic implications. In light of NT revelation, we know that the exodus took place when Christ, the Lamb of God, shed his blood to redeem His elect from spiritual slavery. This exodus would not only have a spiritual dimension, it would be geographical dimension also. Christ stated that the spread of the gospel would begin in Jerusalem, then Samaria, then to the uttermost parts of the earth (Acts 1:7). But what must be noted is that the Apostles faced immediate harsh persecution in Jerusalem, three of them were killed there because of their witness of Christ. In other words, they were fleeing spiritual Egypt-- Israel. Rev. 11:8 gives us the key for understanding this.
8 And their dead bodies shall lie in the street of the great city,
which spiritually is called Sodom and Egypt, where also our Lord was
crucified. (Rev. 11:8)
Now for the symbolism. The number seven is used repeatedly in the Revelation to imply completeness. Notice what's written in Rev. 15:1: ...seven angels having seven plagues, which are the last, for in them is finished the wrath of God. Like the ten plaques that burdened Pharaoh in Egypt, spiritual Egypt would suffer seven plagues that would be worst in devastation. This devastation would bring destruction to their temple, pestilence/disease, and massive loss of life. Jesus spoke of this in Matt 24. They had also been warned centuries before.
58 If thou wilt not observe to do all the words of this law that are
written in this book, that thou mayest fear this glorious and fearful
name, JEHOVAH THY GOD; 59 then Jehovah will make thy plagues
wonderful, and the plagues of thy seed, even great plagues, and of
long continuance, and sore sicknesses, and of long continuance. 60 And
he will bring upon thee again all the diseases of Egypt, which thou
wast afraid of; and they shall cleave unto thee. (Deut. 28:58-60).
John sees what looks like a sea of glass mingled with fire (vs.2). We can only imagine the scenery, because what John described is in heaven. The sea of glass is mentioned in Rev. 4:6, but there's not much information about it. Those who remained faithful, and did not follow the beast (false religion) were seen standing by this sea of glass. What I've written thus far leads to two conclusions. 1. The Song of Moses and the Song of the lamb is the same song in Essence. It's a recapitulation of the slain Lamb's victory before the first exodus at the first Passover, and the divine guidance from bondage, to Christ's ultimate victory at Calvary. 2. In Rev. 15 the faithful stood and sang the Song of Moses and the Song of the Lamb upon exiting spiritual Egypt (by martyrdom) into the beautiful heavenly scene, just as Miriam and Israelites sang it near the earthly Red Sea.