Turned out to be a tough one to find, but still without the originator.
I found your quote on a webpage listing of quotations, but unattributed, at
"A mind can only be opened from the inside."
~ Josh McDowell's "One Year Book of Family Devotions"
"A closed mind is like a spare bed... it's always made up because you never use it."
"I honestly don't believe anyone has a "closed mind" just a wall of self-protection. It can't be "broken down" it has to be eased down from the inside out - for our own sake."
~ posted by "esthechica" on a discussion forum