The phrase “testimony of Jesus” recalls the angel’s words earlier in this verse about “your brothers who hold to the testimony of Jesus.” That testimony (all that Jesus showed John and John wrote down: Revelation 1:1 to the present verse) is now described as “the spirit of prophecy.” And “prophecy” originates from God. Through God’s Spirit, the Lord Jesus revealed to John what would occur in the time between his ascension and his return (Revelation 1:1; Revelation 4:1). So Jesus spoke with God-given authority (Revelation 5:1–14).
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.