Although it is tempting to point out NWT errors based on KIT literal renderings, one should be reminded that accurate translation of any document goes beyond basic meanings, word for word transmission.
Various interlinears have pointed out the dangers of rejecting modern translations based on them. Prepositions, for instance, have a lot of overlap, and the translator must ultimately use his/her understanding of the passage in question to properly convey the meaning into the target language. This explains why we have so many English translations...there are potentially various ways to interpret some biblical accounts, such as Revelation.
The NWT Revised Ed. renders the Greek words in KIT (Rev 20.4), "through [diá] the witness of Jesus and through [diá] the word of the God" as: "for the witness they gave about Jesus and for speaking about God."
The preposition diá with the accusative as it appears in the verse can have a spatial meaning, through, but more likely a meaning of cause: because of, on account of, for the sake of
Bible translator and commentatorRobert H. Gundry explains the clause as: "for testifying about the Testimony who is Jesus and preaching about the Word who is Jesus."
Barclay renders it: "because they had declared their faith in Jesus, and for the sake of the word of God."
Moffatt: "for the testimony of Jesus and God's word"
Goodspeed: "on account of the testimony of Jesus and the message of God"
An Understandable Version: "because they had testified about Jesus and [had proclaimed] the message of God" (Brackets are from translator)
Williams: "for bearing testimony to Jesus and for preaching the word of God"
Weymouth: "on account of the testimony that they had borne to Jesus and on account of God's Message"
NLT: "for their testimony about Jesus and for proclaiming the word of God"
CEB: " because they had told about Jesus and preached God’s message "
GNT: " because they had proclaimed the truth that Jesus revealed and the word of God "
Phillips: " for their witness to Jesus and for proclaiming the Word of God "
NLV: " because they told about Jesus and preached the Word of God "
CEB: " for their witness to Jesus and God’s word "
NWT: "for the witness they gave about Jesus and for speaking about God."