Thinking critically means understanding whether an opinion or argument makes logical sense. There is a difference between critiquing the Bible and applying empirical evidence to highlight parts of the Bible that are false.

Critical thinking requires reason over emotion, recognizing and acknowledging factual evidence, finding the best explanation (not necessarily the most comfortable), and asking questions. It also means changing your viewpoint when shown to be wrong.

Always approach subjects with an open-mind. If you believe with absolute certainty that you are right, leaving no room for doubt, then you have stopped thinking critically. Faith-based thinking is the opposite of open-minded: it purges rationality from thoughts; it favors anecdotes over double-blind, empirical studies based on quantifiable, statistical significance. When you believe something on faith alone, you have shuttered your mind to other answers.

“There is probably no god” means “there is neither empirical evidence nor any logical reason to believe any gods exist.”

Carl Sagan urged people to independently confirm facts, debate, avoid arguing from authority, consider many ideas, quantify, ensure an entire argument works, pick the simpler of two nearly equivalent ideas, and explore theories that can be falsified.