Why should Ishmael sing? This is a common question that gets asked that shows us generally how disconnected we have become with the glory of God and the culmination of redemptive history. The end of all things is worship! Like John Piper says "Missions exists because worship doesn't"
When we look at the Lord's prayer... the will of God that the earth would function like heaven.... so what is the central theme of heaven? It is worship and so one day the earth will get to join in the eternal song and everything that has breath will praise the LORD!
Currently, all over the world five times every day millions of Muslims gather together in a false worship movement declaring that god is not a father and he has no son. There really couldn't be a more dramatic story line as we now see Christians with a Muslim background starting to see Jesus for who He really is and declaring (not just five times a day but unceasingly) that God is their Father and He has a divine Son who is the Jewish Messiah!
As believers we long for the day when the entire earth is caught up into the glory of Jesus Christ and everything that has breath will praise Him! We especially look for the day when the decedents of Ishmael and Jacob start singing with the faith of Abraham to the promised Davidic Jewish Jesus, the King of Kings, and Lord of Lords!
Night and day prayer has exploded across the earth over the last 20 years! Some people estimate that there are some 10,000 prayer ministries that are functioning 24/7! Also the major missions movements of the earth are seeing that prayer and worship is not just a means to salvation but that it is an end in and of itself! The end of the last great harvest will be universal worship from every tribe, tongue, people and nation.
Here is a document outlining in detail the theology of night and day prayer.