BUNYAN's The Pilgrim's Progress (1678) tells the story of "The pilgrim's progress from this world to that which is to come", and describes all the hazards he encountered on the way. The book achieved great success from the start.

By the end of the 17th-century, it became, with the Bible and Foxe's Book of Martyrs, one of the most widely read books in England. The intelligentsia, however, was not at first impressed. Its "homespun style" grated on the sensibilities of the likes of Addison and Pope, being fit only "for maids and apprentices", and the work of a tinker who had neither Latin nor Greek.

Edmund Burke dismissed its "degraded style". Samuel Johnson, however, took it more seriously. "Bunyan's Pilgrim's Progress has great merit, both for invention, imagination and the conduct of the story." He saw the continuing "approbation of mankind" as the best evidence of its worth. "Few books", he added, "have had more extensive sales."

During the latter part of the 18th century, Bunyan's literary reputation grew. The poet and hymn-writer William Cowper called Bunyan "an ingenious dreamer, in whose well told tale sweet fiction and sweet truth prevail . . . whose humorous vein . . . may make the gravest smile."

John Wesley read it on horseback - twice. The Romantics loved it. Robert Southey, poet laureate, brought out a new edition in 1830. In his introductory essay, he described Bunyan as "the prince of all allegorists in prose".

Religious allegory, a pedestrian device in the hands of many writers, in Bunyan's took wing and soared beyond the confines of the Puritan tradition from which it sprang. Coleridge recognised this: "In that admirable allegory, which delights everyone, the interest is so great that [in] spite of all the writer's attempts to force the allegoric purpose on the reader's mind . . . his piety was baffled by his genius, and the Bunyan of Parnassus had the better of the Conventicle."

Delight and humour are not qualities usually associated with religious works. Walter Scott recalled that The Pilgrim's Progress was one of the few reliefs to the gloom of the Presbyterian sabbaths of his childhood.

Charles Lamb was more rhapsodic: at a dinner party, when each guest had to name a person whom he would most like to join them, he chose Bunyan: "If he came into the room, dreams would follow him, and that each person would nod under his golden cloud . . . a canopy as strange and stately as any in Homer."

Perhaps Lamb put his finger on it: the dream-like nature of Bunyan's narrative illuminates its characters with an unearthly light. Christian, Pliable, Obstinate, Faithful, Hopeful, Talkative, Ignorance, and the rest are more than types and shadows: they are the people whom Bunyan had encountered in his journeys as a tinker, and transfigured by his imagination.

The landscape through which Christian travels, with its gloomy mires, dark woods, sparkling streams, and dazzling mountains, is not fairyland: it is the territory of our daily lives, perceived through a visionary's eyes. The reader is drawn into the vision.

The Pilgrim's Progress is not as well known in our generation as once it was, but those who have come to it late, or who now return to its pages, will find themselves in that innumerable company of readers who saw in its story glimpses of the Promised Land, and for whom the trumpets have sounded on the other side.

The Revd Adrian Leak is an Honorary Assistant Priest at Holy Trinity, Bramley, in Guildford diocese.