In his Preface McGrath writes that this biography is based in the first instance on what Lewis himself has written, with the intention of making the development of his ideas the main concern of the book. Fortunately that has not precluded an excellent narrative of many other aspects of the life of this "eccentric genius": this is by no means a purely intellectual history.
Lewis, a voracious reader since early childhood, describes short mystical experiences at the age of about six - one triggered by reading Beatrix Potter's Squirrel Nutkin! But he lost his Christian faith by the age of 17.
There follow fine chapters about Lewis' service in the trenches, his cool relationship with his father, and his unusual one with Mrs Moore (mother figure - and probably more - to replace his own beloved mother who had died when Lewis was nine years old), his studies (Classics and English, winning Firsts in both) at Oxford, his eventual appointment at the age of 26 as a Fellow of Magdalen College to teach English Literature. He was making a name for himself as an academic, but during these years there was no significant development in his attitude to religion. His outlook was rationalistic and he had come to dismiss his childhood glimpses of the ineffable as meaningless.
And then, a third of the way through the book, comes Lewis' conversion. The stimulus for him was the reading of the great writers of the Middle Ages, whose imaginative sense of a unified and cosmic world order was so different from the vision of the essential meaninglessness that had been reinforced by the Great War.
His conversion began with a belief in God in 1930. That was still Theism. But by the autumn of 1931 he had come to accept Christianity. An evening's discussion with his friend J.R.R.Tolkien had made him realize that myths embodied deep meanings; and the myth of Christianity then appeared to Lewis to embody the deepest meaning of all, one that corresponded most closely to reality. By the following summer he had come to accept the divinity of Christ. As secular humanist I have problems with this: valuing myths is one thing, but accepting a myth as a literal truth is quite another.
During the Second World War Lewis became an exponent of Christian belief: in "The Problem of Pain" (1940) he aimed to give a Christian context to human suffering, and its success led to him being invited to be the "voice of faith" in four series of talks for the BBC, and he was also invited to give talks about Christianity at RAF stations. In these talks he found a simple way of talking about religion that could be understood by people who were not academics. The BBC talks were eventually reworked to become in 1952 his famous book "Mere Christianity". In it he produced Christian teaching free of all denominational issues, though the denominations will are necessary to give various elaborations to a common basis and to provide structures which are essential for Christian living. McGrath is good on the strengths and weaknesses of that book.
Before "Mere Christianity" Lewis had published the witty and immensely popular "Screwtape Letters" in which a senior devil advises a junior devil how to lead his patient to our father below. The book brought him fame in the United States. His imaginative approach broadened out into conveying some of his ideas in the form of fiction about other worlds.
Fiction about other worlds was already being written by, for example H.G.Wells, who had used it to promote science as a secular religion. Lewis would use his own novels - beginning with the Ransom Trilogy (1938 to 1945) - to convey a fundamentally religious vision and indeed to show up the some of the dangerously materialist ideas of his time.
As he turned to writing popular books of this kind, he met with much hostility in the English Department at Oxford and Lewis was passed over three times for professorships. (This would contribute to his acceptance in 1955 of a Professorship of Medieval and Renaissance Literature at Cambridge.) Even his friendship with Tolkien cooled: the latter felt that Lewis' creation of other worlds were unacknowledged borrowings from Tolkien's own work. An encounter with the Christian philosopher Elizabeth Anscombe in 1948 made him lose confidence in the reasoning of his academic apologetics for Christianity, and reinforced the turn to conveying his religious ideas in fiction.
And so to the seven "Chronicles of Narnia" novels, written for children, which were published between 1950 and 1956. In "The Lion, the Witch and the Wardrobe", four children cross a threshold into another world which "you cannot forget once you have gone", which helps us "to imagine our world differently". The world of Narnia is only temporarily ruled by the White Witch, but it expects the return of the noble lion Aslan. The theme of the Chronicles, like that of Christianity, is Creation, Fall, Redemption and Final Consummation. Lewis' deep knowledge of medieval and Renaissance literature, of Plato and neo-Platonism, also helped to shape the books.
In 1956, at the age of 57, Lewis married the American Jewish-born ex-atheist, ex-communist and divorcee, Joy Davidson. In 1946 she had been influenced by Lewis' writings to embrace religion and had travelled to England in 1952 with the explicit purpose of establishing a close relationship with him. He found in her an intellectual companion, but it seems that he married her to enable her to stay in England and be allowed to earn a living there. Six months later she was diagnosed with cancer, of which she died four years later. What had begun as a marriage of convenience had become one of love, and Lewis was devastated by her death.
In "A Grief Observed" (1961), he showed how severely his faith was tested, but how he came through it in the end. His own health deteriorated severely in 1961 and he died in 1963.