I’m well aware it’s not an original thought, but as a 13 year old many years ago I was incredibly surprised to find it was one that none of the adults in the church had ever apparently considered or had a response to. The common one was ‘free will exists because God is testing us’ but no one could explain why God would need to test anything when he should already know the outcome, or why he would continue to create people who he knew would fail the test.