I think there's been music in heaven since the day it was created. I also think that, before Jesus came down to earth, the words of the songs that were sung before the throne sounded a lot like the ones found in Revelation 4: Holy, Holy, Holy is the Lord God, the Almighty, who was and who is and who is to come. And, Worthy are You, our Lord and our God, to receive glory, honor, and power; for You created all things, and because of Your will they existed, and were created. Before Golgotha, those in heaven could only praise Jesus for what they knew about Him...that He is the Creator of all things; that He is holy and worthy. But once the cross was set in the ground, and Jesus' death released sin's hold on mankind, I believe the songs in heaven changed.
In Revelation 5, John wept because it seemed there was no one to open the seals to heaven's book; seals that, once broken, would usher in God's judgment upon the earth and take it back to its original state. When one of the elders comforts John, he speaks of the Lion who overcame so as to open the book. And this is where it gets interesting, because I think this is where the new song in heaven begins.
While the 4 living creatures, the elders, and the multitude of angels saw a mighty Lion step forward to take the book--the One who would fulfil prophecy; the Holy and Worthy Creator--John saw a slain Lamb; he saw his Savior, his Redeemer, his salvation. And once his Lamb took the book with the seven seals, the song in heaven changed:
Worthy are You to take the book and to break its seals; for You were slain, and purchased for God with Your blood men from every tribe and tongue and people and nation. You have made them to be a kingdom and priests to our God; and they will reign upon the earth.
It's hard for the one who hasn't received redemption to praise a Redeemer. It's hard to worship a Savior when you've never been saved from anything. Think about it, when the angels went to the first salvation celebration (where we know, from Luke 15, came with a large amount of rejoicing) they were in a "new place" with God. Salvation was a new word. Their roaring Lion had now become a bloody Lamb, and the one standing with them at the throne looked nothing like them. This new citizen of heaven worshiped differently. He cried out with a loud voice, Salvation to our God who sits on the throne, and to the Lamb! I think the angels probably stared in wonder at the sight of his praise; one who stood before them in a robe that had become white because of blood.
And I think that's when heaven's songs changed.
When a heart has been changed, when a soul has been redeemed, when a destiny has been altered, those whose robes have been dipped in the precious blood of the Lamb bow and worship, and they rise to sing a song that all of heaven now joins to sing...Behold the Lamb of God who takes away the sin of the world!
Jesus' sacrifice changed the songs of heaven, and His resurrection changed my song here on earth.
