In The Watchtower Society’s literature from the period of 1975 campaign, at least five times appears a term “must” or “have to be”, which determines what Jesus has to do in connection with the expected Armageddon and the millennial reign. It shows how determined Jehovah’s Witnesses were, who went as far as to enforce their will on God. Here are examples of that:
This would mean that the remnant of these (...) would be sealed (...) the end of six thousand year of humankind’s existence. We are near that point of time now! Bible time-scheduling indicates it. A world storm must therefore be shortly ahead. (Life Everlasting - In Freedom of the Sons of God 1966, p. 357);
That this peace is near is indicated, not only by world conditions, which fulfill Bible prophecy, but also by the fact that six thousand years of mankind’s history is soon to end. It was pointed out that, in ancient Israel, a sabbath day was enjoyed after six days of toil; also that the thousand-year reign of Christ is merely a day from God’s viewpoint. “In order for the Lord Jesus Christ to be ‘Lord even of the sabbath day,’” the speaker declared, “his thousand-year reign would have to be the seventh in a series of thousand-year periods or millenniums.” (Matt. 12:8, AV) That time is near at hand! (The Watchtower September 1, 1969, p. 523);
Further, Bible chronology indicates that we are at the close of six thousand years of human history. For Jesus to be ‘Lord of the sabbath,’ his thousand-year reign would have to be the seventh in a series of thousand-year periods. Would not, then, the end of six millenniums of mankind’s laborious enslavement under Satan the Devil be the fitting time for Jehovah God to usher in a sabbath millennium for all mankind? (The Watchtower September 1, 1970, p. 539);
More recently earnest researchers of the Holy Bible have made a recheck of its chronology. According to their calculations the six millenniums of mankind’s life on earth would end in the mid-seventies. Thus the seventh millennium from man’s creation by Jehovah God would begin within less than ten years. (...) In order for the Lord Jesus Christ to be “Lord even of the sabbath day,” his thousand-year reign would have to be the seventh in a series of thousand-year periods or millenniums. (Matt. 12:8, AV) Thus it would be a sabbatic reign. Since early in the existence of mankind Satan the Devil has been on the loose, making the human family to toil in hard bondage, causing the earth to be filled with violence before the global flood of Noah’s day and inducing the same old earth to be filled with even greater violence today. Soon now six millenniums of his wicked exploiting of mankind as his slaves will end, within the lifetime of the generation that has witnessed world events since the close of the Gentile Times in 1914 till now, according to the prophetic words of Jesus in Matthew 24:34. Would not, then, the end of six millenniums of mankind’s laborious enslavement under Satan the Devil be the fitting time for Jehovah God to usher in a Sabbath millennium for all his human creatures? Yes, indeed! And his King Jesus Christ will be Lord of that Sabbath. (The Watchtower October 15, 1969, pp. 622-623).
The same words appear in a brochure The Approaching Peace of a Thousand Years, 1969, pp. 25-27.
Apart from The Watchtower Society’s statements arguing that the millennium “must” happen after 6,000 years of man’s existence, we have other passages presenting the same teaching, but without that ‘strong’ term. However, it does not change the firmness of predictions. Here are some examples:
It would also be most fitting on God's part, for, remember, mankind has yet ahead of it what the last book of the Holy Bible speaks of as the reign of Jesus Christ over earth for a thousand years, the millennial reign of Christ. Prophetically Jesus Christ, when on earth nineteen centuries ago, said concerning himself: "For Lord of the sabbath is what the Son of man is." (Matthew 12:8) It would not be by mere chance or accident but would be according to the loving purpose of Jehovah God for the reign of Jesus Christ, the "Lord of the sabbath," to run parallel with the seventh millennium of man's existence. (Life Everlasting - In Freedom of the Sons of God 1966, p. 30);
According to the Bible timetable, man’s history on earth has been nearly 6,000 years. Adam was created in 4026 B.C.E., which means that six thousand years of human history end about the fall of 1975 C.E. We are in the great 7,000-year rest day of God, starting at the time he rested after the creation of Adam and Eve. There are, therefore, a thousand years left to run. Without Satan and his demons to disturb mankind it will indeed be a restful time. (The Watchtower July 15, 1967, pp. 446-447);
Within a few years at most the final parts of Bible prophecy relative to these “last days” will undergo fulfillment, resulting in the liberation of surviving mankind into Christ’s glorious 1,000-year reign. (The Watchtower May 1, 1968, p. 272);
Hence, the first six thousand years since man's creation could be likened to the first six days of the week in ancient Israel. The seventh one-thousand-year period could be likened to the seventh day, the sabbath, of that week. - 2 Pet. 3:8. How fitting it would be for God, following this pattern, to end man's misery after six thousand years of human rule and follow it with His glorious Kingdom rule for a thousand years! This Kingdom Christians have prayed for during many centuries. (Awake! October 8, 1968, p. 14);
Actually these six thousand years have been, as it were, man’s workweek, in which he labored by the sweat of his face. But he will get rest during the coming thousand-year reign of Christ, which Bible chronology and fulfillment of Bible prophecy show is to begin very soon. - Gen. 2:3. The seventh one thousand years of the seventh “day” will thus in itself be a sabbath. During it Satan and his demons will be bound. Christ and his anointed followers will rule with him as kings and priests. With what result? That all God’s enemies will be put beneath Christ’s feet. By means of this sabbath the seventh day will truly be sacred, for it will cause righteousness to flourish. (The Watchtower February 15, 1970, p. 120);
However, Bible chronology which indicates that Adam was created in the fall of the year 4026 B.C.E. would bring us down to the year 1975 C.E. as the date marking 6,000 years of human history with yet 1,000 years to come for Christ’s Kingdom rule. (The Watchtower May 1, 1970, p. 273).
It seems it is worthwhile to check how often appear such words describing ‘the end’, as Armageddon, ‘day of Jehovah’, ‘millennial reign’, destruction, etc. in The Watchtower Society’s publications published in the period of 1975 campaign, before it and after it.
Here is a sample: the word “millennium” used 1960-1977 only in The Watchtower magazine (according to results showed by CD Watchtower Library - 2005 Edition 2006):
1960 - 2
1961 - 1
1962 - 1
1963 - 2
1964 - 2
1965 - 2
1966 - 0
1967 - 37
1968 - 14
1969 - 24
1970 - 2
1971 - 1
1972 - 0
1973 - 0
1974 - 8
1975 - 24
1976 - 2
1977 - 0.
We see from the above that especially in the years 1967-1969 and 1974-1975 the word “millennium” was a pet term, used by The Watchtower Society. We will stop with that one word, because there are many such key words, and such issue would require deeper inquiries and research.