C.S. Lewis was saying there is nothing in this world that will fill the emptiness in your soul — no sexual experience, no drug high, no relationship, no amount of success, no quantity of money, no accumulation of possessions. And even if you did possess all of those things at this moment, there still would be something in the deepest part of you that realizes there is more to life than this. The real thing that Lewis was alluding to is the very thing for which we were created. It is that drive to know the God who made us.
John 17:3 says, “This is eternal life, that they may know You, the only true God, and Jesus Christ whom You have sent.”
– Essentials 2 by Greg Laurie