You've heard of hard hearts, but what about hard minds?
Concrete minds can be a special problem among Christians.
They form when we hear a teaching, combine it with personal prejudices, and let it harden into concrete.
These concrete thoughts become "Scripture" to us and we'll defend them no matter how many Bible passages refute them (Colossians 2:8).
Frequently when I write about Biblical judgment, I encounter folks with "Judge Not!" concrete thoughts. No matter how much Scriptural evidence I supply, they continue to insist that the Bible teaches we must never judge anyone or anything.
Over the years, I've learned that, if I'm not careful, I can pour cement in my brain too.
It's so important that we check every teaching with the full context of Scripture instead of highlighting a few passages (Acts 20:27). And it's important that we never trust others to do our studying for us (2 Timothy 2:15).
Concrete is great for a patio but not for a mind.