Revelation 15:3

Revelation 15:3 And they sing the song of Moses, the slave of God, and the song of the Lamb, saying, Great and wonderful are Your works, Lord God the Almighty! Righteous and true are Your ways, O King of the nations! 

Footnote on "song"

The song of Moses, indicating God's triumphant judgement over the enemy of His people, praising God for His judgement, which is on the negative side; whereas the song of the Lamb, indicating Christ's redemption experienced by God's people in the presence of their enemy, praises God for Christ's redemption, which is on the positive side. The late overcomers are positioned to stand on the glassy sea because of two facts: 1. God's judgement over the enemy and 2. Christ's redemption for God's people.