We would repeat John’s declaration. It seems that in order to prevent any misunderstanding as to the meaning he gives to the expression, the beloved apostle makes the matter unmistakably clear when he gives us the following equivalent statements: “I am thy fellowservant, and of thy brethren that have the testimony of Jesus.” Revelation 19:10. “I am thy fellowservant, and of thy brethren the prophets.” Revelation 22:9. EGWC 557.2
Here the testimony of Jesus is linked with the work of the prophets of God in a way that surely cannot be misunderstood. This fact, together with others already mentioned, should enable us clearly to understand why, in Revelation 19:10, “the testimony of Jesus” is called “the spirit of prophecy.” EGWC 557.3