“In modern times, nearly all scholarly authorities on the book of Revelation have interpreted the speaker in Rev 1.8 as God the Father, not Jesus Christ.”
(Kermit Zarley, “Is Jesus ‘the Lord God ... The Almighty’ In Revelation 1:8?”)
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The footnote Zarley provides contains some examples of trinitarian scholars who affirm that the speaker is the Father, not Jesus.
If it were a certainty that Jesus is the speaker in Revelation 1:8 these trinitarian scholars - every one of whom affirms the Nicene Creed - would not make this concession to Jewish monotheism.
(Kermit Zarley, “Is Jesus ‘the Lord God ... The Almighty’ In Revelation 1:8?”)

Is Jesus “the Lord God ... The Almighty” In Revelation 1.8?
Most distinguished commentators on the book of Revelation claim its first chapter in v. 7 tells about Jesus, but in v. 8 the speaker is God. And the Bible calls God "Almighty" seven other times, but it never calls Jesus that.

The footnote Zarley provides contains some examples of trinitarian scholars who affirm that the speaker is the Father, not Jesus.
If it were a certainty that Jesus is the speaker in Revelation 1:8 these trinitarian scholars - every one of whom affirms the Nicene Creed - would not make this concession to Jewish monotheism.