The previous chapter told us about the events that happen on Earth when Satan and his demons are cast out of heaven. Chapter 15 gives us information about the great harvest of souls on Earth that happens as a result of the great tribulation that Satan brings on the Earth.

Some say that the 144,000 in verse 1 are different people than the 144,000 in Rev. 7:4, but most conservative Bible scholars believe this is the same 144,000 that were sealed on the Earth. They have the name of the Father and the Son written on their foreheads because they descended from Israel and are disciples of Jesus. The Lamb stands on Mount Zion with the 144,000 Jews who walk in His footsteps. Jesus is in the Holy City called Mount Zion (Psalms 48:2). There is a Mount Zion on Earth as well, but its clear that they are in the Holy Heavenly City.