Revelation 15:3

And they sing the song of Moses the servant of God
Not that in ( Deuteronomy 32:1 ) but that in ( Exodus 15:1 ) and the sense is, either that they observed the law of Moses, which he as a servant in the Lord's house faithfully delivered, and kept it distinct from the Gospel, and did not blend them together, as in the times before; or rather, that they sung a song like that of Moses, and on a like occasion. Pharaoh was the very picture of the pope of Rome; his oppression and cruel usage of the Israelites represent the tyranny and cruelty of the Romish antichrist; and the deliverance of Israel out of Egypt, and the destruction of the Egyptians at the Red sea, which occasioned the song of Moses, were an emblem of God's bringing his people out of antichristian bondage, and of the ruin of antichrist, upon which this song is sung; and Rome, in this book, is called Egypt, ( Revelation 11:8 ) . The Jews have a notion, that the very song of Moses itself will be sung in the world to come, in the days of the Messiah; for they say, there are in it the times of the Messiah, and of Gog and Magog, and of the resurrection of the dead, and the world to come ^F12. And this song was sung by the Levites in the daily service ^F13.

And the song of the Lamb;
the Lamb of God, who was slain for the sins of men; the same song of which mention is made, ( Revelation 5:9 ) ( 14:3 ) the song of redeeming love, a song of praise for the blessings of grace which come through him, and of deliverance by him:

saying, great and marvellous are thy works, Lord God Almighty;
Christ is in this song addressed as a divine person, as Lord of all, God over all, blessed for ever, the Almighty God, as his works declare him to be; his works of creation, providence, and redemption, which are all great and marvellous, particularly the accomplishment of the glorious things spoken of his church, and the destruction of his enemies, which are here designed:

just and true are thy ways, thou King of saints:
made so by his Father, and acknowledged by all his people, and especially at this time, when his kingdom will more visibly and gloriously appear: the Alexandrian copy, one of Stephens's, the Complutensian edition, and Arabic version, read, King of nations, as in ( Jeremiah 10:7 ) from whence this, and the beginning of the next verse, seem to be taken; the Vulgate Latin and Syriac versions read, "King of ages", an everlasting King, as in ( Jeremiah 10:10 ) but the generality of copies read as we have it: and the ways of this King are just and true; his purposes, decrees, and counsels of old, are faithfulness and truth; all his proceedings towards his own people, his subjects, are mercy and truth; his precepts and ordinances, his worship and service, are just and true, in opposition to every false way; and all his judgments upon his enemies, which are intended, are just, being what their sins deserved, and are true, being agreeably to his word and threatenings.