Reason and imagination were important to Lewis because they had once been separated in his own life but were later brought together. For him, meaning often came through imagination. For some, imagination can seem like an escape from reality. In contrast, Lewis believed that stories can be an escape into reality. Imagination is a means to truth.
As part of Lewis' conversion, he received what he later called the "baptism of his imagination." He came to see that his earlier aspirations pointed to something real, unlike his atheism which led him to a grim and meaningless universe. He noted that the authors with the most depth in them were written by people of faith while the rest were 'tinny' - entertaining, but hardly more. Imagination opened his mind to the beauty of the holiness around him and ultimately to the beauty of the holiness in God.
Lewis believed that adults should keep a childlike outlook on the world. This included a tireless curiosity, an intensity of imagination, the faculty of suspending belief, an unspoiled appetite, and a readiness to wonder, pity and admire. Through good stories, he believed that we could escape to reality - to see how the human life might be lived, perhaps ought to be lived.
God is the great creator, but he delegates creativity to us as well. Tolkein and Lewis talk about our role as 'sub-creators.' Only God creates something out of nothing, but we can use our creativity to create something out of something.
We often learn by seeing - catching a vision. Read good stories - feel and experience the world through the author's eyes. Travel to places you have never been, experience things you have never guessed, struggle with dilemmas you have not faced, and learn how people of other cultures deal with life.
[Summarised from Chapter 7 of Art Lindsley's C.S. Lewis' Case for Christ]
Next: Objection #6 - Miracles.