Their worship of God came complete with the posture of prostration, falling with their faces to the ground, as was their habit (Revelation 4:10; Revelation 5:8, Revelation 5:14, Revelation 7:11; Revelation 11:16). With that action they are giving expression to the greatness and Godness of God inasmuch as they (creatures!) are unworthy to exist in his presence. Their adoration for God, then, is communicated not just in words but first in posture (and hence reflecting an inner attitude).
4 And the twenty-four elders and the four living creatures fell down and worshiped God who was seated on the throne, saying, “Amen. Hallelujah!”