Walter Jackson Bate, John Keats
(1963; rpt. New York: Oxford University Press, 1966), p. 28:
The larger gain in this reading was simply that a door was openedthat its opening was sensed so powerfully that henceforth the open door, the open window, became a haunting metaphor to Keats. For it brought the vital discovery (though there might be a few years before he realized it) that we are not completely the creatures of the environment in which we are placedthat we need not be imprisoned by the room where we are, by the stock responses we pick up from those about us, but that there are openings to something more spacious through the large written record of the past that we call literature.