Thinking is reserved for humans. Dogs and cats do a primitive form of it, but not like humans. Humans have the ability to assimilate information, then discriminate and decide in regard to it. All the mental faculties come into play in thinking– the intellect, the will, even the emotions.
Those claiming to be Christians will make the claim on the basis of what they believe the Scriptures teach. This is so, regardless of how far right or left on the spectrum of thought they find themselves. This is not to say that all interpretations are correct or that as long as they make the claim, they are fine. It's just a starting point.
I was talking to a preacher about his work in a small, struggling congregation. There had been plenty of 'ups and downs'. I've admired his work there for some time and told him so. His response impressed me. He said, "it's ditch-digging work." By that he meant his work was not flashy or spectacular. There wasn't any glamour or personal glory to be gained. He wouldn't develop a big reputation from what he was doing.