Chapter XV: The Beginning.
Lewis was not a Christian at this time. He believed that there was a God and that his commands should be followed just because he was God. There was no belief that there was reward or punishment involved, something Lewis is grateful for. "To know God is to know that our obedience is due to Him.'
His transition from Theism to Christian is fuzzy in his mind. "If Theism had done nothing else for me, I should still be thankful that it cured me of the time-wasting and foolish practice of keeping a diary." He did start attending church and college chapel. He thought one should "fly one's flag." But he wasn't a fan of church. He hated (at that time and later)hymns and never liked the organ. Churchgoing was symbolic and he is not aware that it helped move him to Christian.
He knew fro mhos literary criticism work that the gospels were not myth. They did not read like myths, nor did they read quite like history. The depiction of Jesus was unique, recognizable, yet numinous. As he continued the journey towards Christianity, he felt a resistance almost as strong as his resistance to Theism.
He set out to a zoo one morning as a non-Christian. When he reached the zoo he did. He didn't spend the journey in thought. He wasn't emotional about it. It was more like awakening after a long sleep and realizing that you are awake.
The whole pursuit of joy which drove him for many years lost interest for him after he became Christian. It was only valuable as a pointer, much like a road sign when you are lost. But, if you know where you are going, you can ignore the signs and proceed on your journey.