The Watchtower teaches that the two witnesses dressed in sackcloth, which are depicted in Revelation preaching for 42 months, was fulfilled by the International Bible students during the First World War.
The 12th paragraph of this week’s lesson states: "The John class had to preach this message for a definitely stated time: 1,260 days, or 42 months, the same length of time that the holy city was to be trampled underfoot. This period seems to be literal, since it is expressed in two different ways, first in months and then in days. Additionally, at the beginning of the Lord’s day, there was a marked period of three and a half years when the hard experiences of God’s people matched the events prophesied here—starting in December 1914 and continuing to June 1918. They preached a “sackcloth” message concerning Jehovah’s judgment of Christendom and the world."
Just how it is that the Bible Students may have preached in sackcloth is not clearly explained. In reality, the activity of the Bible Students during the period from 1914 through 1917 does not appear to have been very much different then during the period prior to that time. In fact, the Watchtower even admits as much. For instance the Kingdom Proclaimers book states on page 423: “During the early years of the war, there was little hindrance except in Germany and France. Tracts were freely distributed in many places, and there was continued use of the “Photo-Drama,” though on a much more limited scale after 1914.”
The release of the Photo-Drama of Creation in 1914 was really the pinnacle of the Watchtower Society’s efforts to educate the public. And as the Proclaimers book acknowledges, the Photo-Drama was presented to audiences in America and Europe, with two notable exceptions, all during the period of the First World War. So, if the Society was the embodiment of the symbolic “two witnesses” there is simply no evidence that they were made to preach in a mournful and lowly state, as is symbolized by the sackcloth.
The truth is, the Society’s 1914 teaching and the interpretation of the two witnesses of Revelation are merely artfully contrived false stories. (See commentary: Do you believe the Lie?)
For a fuller discussion of the two witnesses see the article The Revelation of Christ and the Two Witnesses.