I've not read Elaine Pagels' new book on Revelation, but Adam Gopnik reviews it in the New Yorker. Pagels apparently argues that the book of Revelation is an argument against the Pauline form of Christianity that was emerging out of the first century.
"...it was written by an expatriate follower of Jesus who wanted the movement to remain within an entirely Jewish context, as opposed to the 'Christianity' just then being invented by St. Paul..."
In any case, Gopnik says that the inclusion of Revelation came at the insistence of Athanasius in the fourth century. Says he:
Revelation very nearly did not make the cut. In the early second century, a majority of bishops in Asia Minor voted to condemn the text as blasphemous. It was only in the three-sixties that the church council, under the control of the fiery Athanasius, inserted Revelation as the climax of the entire New Testament. As a belligerent controversialist himself, Pagels suggests, Athanasius liked its belligerently controversial qualities.
This is some different than the case made by David Dungan in Constantine's Bible. He argues that it was Eusebius of Caesarea who created a process for determining the books of the Christian canon. Eusebius essentially took a poll of the writings of the early church fathers--the ones earlier than him--and, if a book was universally accepted as "orthodox" it was included. If a book was argued about, it was put in the "disputed" category.
Eusebius included the book of Revelation, even though accepting it meant going against his own system. After noting that Revelation was accepted by some, but disputed by other church authorities, he went ahead and included Revelation anyway, an inclusion that was "entirely inconsistent" with his own method, says Dungan. (p. 71)
So who is responsible for the inclusion of Revelation? The acerbic fanatic Athanasius, or the wily academic Eusebius? You can see the motivation of Athanasius. The pitched battles of Revelation reflected his own personal battles with (people he designated as) heretics. The enigmatic Eusebius' motivation is less clear.