@Rebelofnj,
Have you read Planet Narnia by Michael Ward? It’s really good. It’s a doctoral thesis about the third meaning in the Narnia books. As Lewis was an Oxford don and not just a kid’s author people have been looking for this for a long time. The first being the story, and the second being the Christian allegory, but the third has remained a mystery.
Ward has found it, the seven books are linked to the seven days of the week and their respective planets. Lewis was a Medieval scholar and these are the seven planets as someone in the Middle Ages would see them.
The seven planets are the Sun, the Moon, Mercury, Venus , Mars, Saturn and Jupiter. Each of the books is looked at as one of the planets. It’s very convincing, and a good read. It’s quite wide ranging and looks at other works outside of Narnia like Screwtape and the science fiction pieces.