Of course I studied the Bible to gain a solid Scriptural understanding, but Lewis's books gave me the hunger to learn more.
So you think this “you were meant for greatness” stuff is actually Scriptural? I’m glad I scare people with such a mindset away. Jesus scared a lot of them away too, when their reasons for following him were shallow.
You erroneously assume that anyone who believes that following Christ leads to greatness must have been motivated to follow him for that very reason. That is wrong of you.
You also, to you own detriment, ascribe a worldly definition to "greatness". I want to do great things in Christ, whether that be quietly raising my children to love the Lord, or becoming the next Billy Graham. The former would certainly not be considered "great" by the world, but if it is God's calling for me, then it is the greatest thing possible.
It's a shame that Scripture wasn't enough for you to do this.
I've read and thoroughly enjoyed Lewis's books. I love his writing. He is thought provoking. But he is also inclusivist. Lewis is not Scripture and shouldn't be wasted time on in church. However it is certainly worth reading all kinds of stuff (within reason - e.g. not worth reading playboy 'for the articles.') as long as you realize that where it doesn't line up with Scripture, it is just plain false.