Why do Jehovah’s Witnesses cite William Barclay as to the identity of the speaker in Revelation 22:13 knowing he believed it is Jesus?

@Mr. Bond Please note that in the article that you cite from the JW.org website states,

Commenting on this section of Revelation, Professor William Barclay wrote: "Things are set down without any apparent order; . . . and it is often very difficult to be sure who is the actual speaker.” (The Revelation of John, Volume 2, Revised Edition, page 223) Thus, “the Alpha and the Omega” at Revelation 22:13 can be identified as the same Person given this title elsewhere in Revelation​—Jehovah God.

The article is using the statement that "Things are set down without any apparent order" to further reiterate that no one knows for sure who is actually speaking. And for that reason the article says,

“the Alpha and the Omega” at Revelation 22:13 can be identified as the same Person given this title elsewhere in Revelation​—Jehovah God.

So they are making a logical conclusion based on other scriptural evidence and not making a supposition based on a whim.

Incidentally Barclay is frequently quoted by JWs. In fact a quick search of his name on Watchtower Libray comes back with 37 occurrences. While true that he identified the speaker in Revelation 22:13 as Jesus it is also true that he says it is difficult to be sure and also true that Barclay said Jesus is not God.

This begs the question: How can Jesus be identified as the Alpha /Omega by Barclay on the one hand and be said not to be God on the other? JWs consistently identify Alpha/Omega only as Jehovah God.

First, let me answer your question near the end of your comments, and then I will be able to give a swift, simple answer to your question in the heading. You asked near the end, “Why do the Jehovah Witnesses quote Professor William Barclay saying "it is difficult to be sure who is the actual speaker?"

The first point to make is that establishing who the actual speaker is in verse 13 is not clear-cut. More than one speaker speaks in chapter 22, from when the epilogue starts (verse 6) to the last verse (21).

Verse 6 starts, “And he said unto me…” (unto John, that is. I won’t include John’s comments in these verses, as those are clearly identified.) Verses 7 and 12 say, “Behold, I come quickly…”. Verse 13 says, “I am Alpha and Omega, the beginning and the end, the first and the last.”

It is legitimate to ask whether there are two, or three heavenly speakers here, because there were no inverted commas in koine Greek, to help distinguish one speaker from another. This is where translations like the Authorised Version openly show the nature of the difficulty, not having inverted commas. But some translations, like the Jehovah’s Witness New World Translation, do insert inverted commas, which demonstrate their belief that a third heavenly speaker breaks into the dialogue – they would say that the new speaker from verse 12 through to the end of verse 15 is Jehovah God.

But trying to identify various speakers in the epilogue, without reference to the preamble (chapter 1 verses 1 to 3) and everything from there to the epilogue is ridiculous and, thankfully, you do not ask us to make any identifications of speakers in chapter 22. However, anyone who has studied the whole book of the Revelation will know that it is neither chronological nor literal. And chapter 22 deals with future events. Therefore, anyone who claims that it is difficult to be sure who the speaker is in chapter 22 verse 13 is being honest. As was William Barclay in that partial quote by the Watchtower Society.

The reason why they gave that partial quote was because they hoped it would substantiate their argument for claiming the speaker there to be Jehovah God. Unfortunately for them (as you proved in your comments) Barclay came to the conclusion that it was Jesus speaking, so all that can be claimed from Barclay’s quote is that he found it difficult to state who the speaker was in verse 13 even though, on balance, he came down on the side of it being the resurrected Christ.

Now the answer to your main question: "Why do Jehovah’s Witnesses cite William Barclay as to the identity of the speaker in Revelation 22:13 knowing he believed it is Jesus?" To be charitable, we cannot state that the anonymous writer who incorporated that partial quote of Barclay knew that Barclay believed it to be Jesus. He may not have done any research into Barclay’s other comments about what Jesus said in the book of the Revelation. Perhaps he was under instructions to pick quotes from various theologians that could pad out the Watchtower article, to encourage readers to think that ones such as Barclay concluded the same as the Watchtower Society (when he did not.) Certainly, the wording immediately following Barclay’s partial quote easily lends itself to the erroneous idea that “Thus, ‘the Alpha and the Omega’ at Revelation 22:13 can be identified as the same Person given this title elsewhere in Revelation—Jehovah God.”

At risk of sounding uncharitable now, I would say that from my experience of the amount of checking up on Watchtower quotes that rank and file Jehovah’s Witnesses do, very few of them would even try to get hold of Barclay’s writings, to see if he had been quoted out of context or not. Indeed, it has only been in comparatively recent years that the Watchtower Society has ensured that full citation references are given when it quotes others, to enable their readers to check, should they so wish. I have a considerable library of their books, and hundreds of their magazines (up till the turn of the century) and I was almost never able to chase up quotes purely via their literature. Even with the advent of the Internet, it still remains a hugely time-consuming task to get a full quote without a precise source and page number given. But as the full citation for Barclay's partial quote was given in that Watchtower article, any diligent Jehovah’s Witness can do a check and discover for themselves what appears to be a somewhat misleading misconstruction of Barclay, to make it seem as if he agreed with the Watchtower Society re. Rev. 22:13, when he actually disagreed. And if anyone thinks I am being uncharitable here, please just check out for yourself by researching Barclay, as I have done on such matters. He is now dead, so cannot defend himself from misleading applications of his work, which I think this is an example of. But Jehovah’s Witnesses will disagree, which they are entitled to do. After all, this is a matter of interpretation of one of the most profoundly symbolic and prophetic parts of the Bible. Nevertheless, scholastic integrity requires honest representation of those quoted, and not partial quotes that are not balanced by more quotes that would lead to a different conclusion.