Was CS Lewis an evangelical?
I think we can say categorically that he was not. Of course, he was a man of his generation. He denies being a fundamentalist, although he was accused of it because he refused to categorize any narrative as unhistorical because it contained miracles. Some people found miracles so hard to believe that they could not imagine any reason for CS Lewis to believe them other than a belief that every sentence of the Old Testament has historical or scientific truth. But this went much further than he would go. He was a creationist, but not a six-day creationist, but he also believed in purgatory (largely because he could not conceive that a sinner like him should be let into heaven without some serious scrubbing).
His profession was literary criticism and he applied his techniques to the Bible. His prejudice was that it was true, but he recognised different types of truth. Take the book of Job, for example. Along with Jean Calvin, he doubted whether it was historically true, rather than a work of fiction, like the Prodigal Son or the Good Samaritan, told to make an important point. He would not say it was not historical, but Job has no connection with any history or even legend, with no genealogy, living in an undescribed country, and the story is written as a storyteller would tell it.
He would accept that some early stories of Genesis come from an oral tradition and may have altered over time. We know that the Jews took inordinate means that the written text was preserved intact, though was there a time when alterations in the oral tradition could have been interpolated? But he also believed that the Holy Spirit took tremendous trouble to preserve his message in Scripture, through the agency of the church. This means that he has a greater respect for the Catholic church than we evangelicals might have. He says elsewhere that the differences between different branches of the church might turn out to be mere semantics when we get to heaven.
I would not be too quick to criticize other Christians and the grounds of semantics.
I quote from Reflections on the Psalms. "We may observe that the teaching of Our Lord Himself in which there is no imperfection, is not given us in that cut-and-dried, fool-proof, systematic fashion we might have expected or desired. He wrote no book. We only have reported sayings, most of them uttered in answer to questions, shaped in some degree by their context. And when we have collected them all, we cannot reduce them to a system. He preaches but he does not lecture. He uses paradox, proverb, exaggeration, parable, irony; even the 'wisecrack'. He utters maxims which like popular proverbs, if rigorously taken , may seem to contradict one another. His teaching therefore cannot be grasped by the intellect alone, cannot be 'got up' as if it were an academic subject. If we try to do that with it, we shall find Him the most elusive of teachers. He hardly ever gives a straight answer to a straight question. He will not be pinned down. The attempt is like trying to bottle a sunbeam."
I take this to mean that Lewis thinks that the Scripture is much more dynamic than we evangelicals take it to be. It is more open to interpretation guided by the Holy Spirit and that there are still truths to emerge that are not in the commentaries.
I think he would say that the New Testament characters acted in just this way. For example with the two on the road to Emmaus Jesus taught what it said about Himself from the Pentateuch and the prophets. Before Jesus much of what he revealed would have been interpreted differently by the Jewish teachers. Undoubtedly there are Messianic passages , but would the suffering servant have been seen as Messianic? Probably not.
But we have Phillip opening up Isaiah 53 directly with Jesus in mind to the Ethiopian eunuch. Before that passage in Acts, the suffering would have been thought of as referring to the nation of Israel itself. Jesus identified himself with the sufferer in Psalm 22 (My God, My God, why hast thou deserted me ... ) He asks how Christ could be both David's son and David's lord identifying himself as 'my Lord' in Psalm 110. He applied Psalm 91:11-12 to himself (He shall give his angels charge over thee ... that thou hurt not thy foot against a stone.) Psalm 118:22 (neither shalt thou suffer thy Holy One to see corruption) is appropriated as a prophesy of the resurrection in Acts 2.
Most have difficulty with uncertainty. With Scripture, I am afraid that we have to live with uncertainty. Even the most convincing commentater will admit to pasages with alternative explanation. No systematic theology is entirely convincing on every point. Lewis is vaguer than most and leaves many points undetermined, yet what he is sure about he puts beautifuly clearly. There has been too much Lewis worshipping for my taste and he would have hated it. He regarded himself as an amateur theologian and a professional student of literture, especially teh ancient literature of many traditions. He brought that studen's eye and insight into his studies of Scripture and he was always open to another interpretaion. I admire his intellect and his writing style, but I know he could sometimes be profoundly wrong.