Source: H. Graetz, History of the Jews, volume II (Philadelphia: Jewish Publication Society of America, 1893) 167-168.
"[Jesus' disciples] believed that some then alive would not taste death until they had seen the Son of Man enter his kingdom. His disciples were hourly expecting the return of Jesus...This kingdom was to last a thousand years: the Sabbath year of jubilee, after the six thousand years of the world, would be founded by Jesus when he returned to earth, bringing the blessing of peace and perfect happiness to the faithful."
The Armstrong movement often taught the seven thousand year plan. It pointed out that the week has six days of toil and labor, with a Sabbath of rest on the seventh day. According to the Armstrongs, this pattern existed on a larger scale as well. God has given human beings six thousand years to toil and live independently of God. Then, Christ will return and establish a millennium of rest, peace, and joy. They based their belief on verses like Psalm 90:4 and II Peter 3:8, which say that a day in God's eyes is like a thousand years. And the founder of the Jehovah's Witnesses, Charles Taze Russell, supported this notion with Romans 8, which affirms that the earth is in bondage and suffers labor pains. He likened that condition to the six days of labor.
The first-second century Epistle of Barnabas has a similar view, which is articulated in Barnabas 13:4-6. But I'm puzzled: if the early Christians believed that Jesus was coming soon, how could they also maintain that he would return six thousand years after the creation of the universe? Most calculations place that date in the twentieth or twenty-first century, basing their conclusions on biblical chronology. Did the author of Barnabas see things differently?
If Barnabas is a late book, as in from the second century C.E., then my dilemma is not as bad, or so it would seem. According to some scholars, the second century was a time when people didn't really expect the imminent return of Jesus Christ. That was the historical context of II Peter's remark about a day in God's eyes being as a thousand years. Christians by that time pushed the date of Christ's return far into the future, since Christ hadn't come back yet.
Yet, the above paragraph is rather simplistic, for we find an imminent expectation of Christ's return in second century sources. The Shepherd of Hermas warns Christians to repent, since the time for repentance will soon come to an end. And Barnabas 3 appears to have an imminent expectation, which is why he exhorts and warns his fellow Christians.
So how did Barnabas reconcile his belief in Jesus' imminent return, with his notion that Christ would return in the seven thousandth year? I have no idea.