In his book Postmillennialism: An Eschatology of Hope, (Phillipsburg: P&R Publishing, 1999), Keith Mathison says this:
…postmillennialism teaches that the “thousand years” of Revelation 20 occurs prior to the Second Coming. (10); An essential doctrine of postmillennialism is that prior to the Second Coming, the messianic kingdom will grow until it has filled the whole earth. (191)
This is why Mathison cannot accept preterism: there is no room for his millennium which has already spanned more than 1,900 years; and there is no sign this bloated era is about to end anytime soon. Mathison despises the preterist position so much, he edited another book devoted to debunking it (When Shall These Things Be? [Phillipsburg: P&R Publishing, 2004]). However, he, evidently, became so confused with the task he ended up debunking postmillennialism instead. In 1 Thessalonians 4, Paul refers to the “coming of the Lord” and twice uses the phrase “we who are alive and remain” (1 Thess. 4:15, 17). Clearly, Paul thought he might be alive until the second coming. This is not something one would expect a postmillennialist to admit. However, amazingly, Mathison does. He writes,
“As far as Paul knew, Christ could have returned in his lifetime” (194).
What is Mathison thinking? Does he not recognize the implication? If Paul thought Jesus could have returned within his lifetime, there is no way he could have believed in the postmillennialism Mathison promotes. If Paul was a Mathison-style postmillennialist, he would not have expected the second coming for at least a thousand years! So, with one sentence, Mathison has obliterated postmillennialism. A few pages later, he reiterates his previous position contradicting himself again:
When the word “thousand” is used in Scripture, it refers to a literal thousand or to an indefinite, but very large, number. (209)
It doesn’t take great insight to see that if Paul thought Jesus “could have returned within his lifetime,” then, obviously, he did not foresee the “very large number” of years required to fill “the whole earth” with the messianic kingdom; and if Paul didn’t know anything about an enormous millennium, it’s hard to believe that any of the other apostles did. In fact, we know they didn’t. See The Apostles Predicted a First-Century Return of Christ.