That instruction is the corrective John needs after his prostration in front of the angel. The uniform theme of Revelation 19:1–5 (in response to the fall of Babylon) was Hallelujah!
(Praise the Lord!) John himself needs to participate in that worship!
10 Then I fell down at his feet to worship him, but he said to me, “You must not do that! I am a fellow servant with you and your brothers who hold to the testimony of Jesus. Worship God.” For the testimony of Jesus is the spirit of prophecy.