"Getting it"

There's something I've struggled with for a very long time. In light of some conversations I had today, and the link I found to Ben Stein's movie, I just don't understand how people can be so ignorant.

A large portion of the people in the US would say they either believe in God, or they are Christian, but many of their lives bear no fruit. One of my family members (an older member) grew up in the church of fire & brimstone. He attends church every Sunday, but appears to merely hold down the pew. He has lived a great life, and I have a lot of respect for him. My fear is that he just doesn't understand about being 'saved'. Several family members have tried to broach the subject, but he's not receptive.

I'm just confused as to how so much evidence can be there, and be very clearly true, and yet people just don't understand it. I'm think it has something to do with having a hardened heart, I just wish I better understood what is happening.