the twenty-four elders
The elders were first seen seated on thrones around Gods throne (Rev. Rev. 4:4+). They are probably representatives of the Church. See commentary on Revelation 4:4.
the four living creatures
The four living creatures were first seen by John in the midst of the throne. They are of a high angelic order, probably cherubim. See commentary on Revelation 4:6.
fell down and worshiped God who sat on the throne
The scene is much like that which John first saw when he was transported to heaven in the Spirit to see the twenty-four elders and living creatures worshiping before Gods throne. The elders are found near the throne and continually falling in worship in recognition of the great acts of God. When John first saw the elders, they were falling before God, casting their crowns before the throne, and extolling His greatness in creation (Rev. Rev. 4:10+). Later, when the Lamb took the scroll prior to loosing its seals, the elders fall in worship and adoration while singing a song of redemption (Rev. Rev. 5:7-9+, Rev. 5:14+). When the great multitude who came out of the Great Tribulation give praise to God and the Lamb, the elders fall on their faces in worship (Rev. Rev. 7:9-11+). At the sounding of the seventh trumpet, when the kingdoms of this world are declared to have become the kingdom of God and His Christ, the elders fall in worship (Rev. Rev. 11:15-16+). The participation of the elders falling in worship here indicates the great importance attached to the destruction of Babylon by heaven. God gains glory by her destruction, an important step on the way to establishing the Millennial Kingdom on earth.
Amen means truly, as when expressing agreement. See commentary on Revelation 3:14. Alleluia means praise God. See commentary on Revelation 19:1. The elders and living creatures agree with the statement of the multitude and add their own praise.