"I am not an economist and I simply do not know whether the investment system is responsible for the state we are in or not. This is where we want the Christian economist."
The context is whether borrowing/lending at interest is okay even though it appears to be forbidden in Scripture. Lewis' point is that we need laypeople like Christian economists to help us explain and apply the Scripture in our modern day context.
The answer, as we fleshed out in class, is "Yes, it's okay." The students initially seemed mostly uncertain about Scripture's implications. James Halteman, a Christian economist at Wheaton, did a fantastic job in his book of explaining how the interest of the Bible is not the same as interest in today's capitalism. I found other essays written by Christian economics/finance people that dodged the subject.