Had the privilege of standing in my home church's pulpit recently, and declare the truth of God's Word. At one point I rehearsed again a life principle that I've shared through the years every chance I get:
when it comes to authority related to spiritual truths, everyone is staking his/her eternal destiny on one of two bases--- revelation or speculation.
In other words, when considering such questions as, "What happened before I was born?", and, "What will occur after I die?", and, "Is there a heaven, and, if so, how can I go there when I die?", there are only two options upon which we all depend for our answers: a supernaturally-revealed answer we accept, or our best guess.
A classic example is creation vs. evolution to explain the origin of the physical universe. Although perhaps the evolutionist would hotly contend that he is not speculating, in point of fact he was not there to witness the beginning. The creationist insists that, although he, too, wasn't present the moment it all occurred, his basis of authority is the supernatural revealing of the origin of our universe by the One Who was: the unchanging, living God Who created it all ex nihilo, from nothing. How revealed? By His breathed-out Word, the Scriptures.
Thus, the evolutionist places faith in implications (speculation) drawn from observable evidence, whereas the creationist places faith in the trustworthy Word of the One Who, transcending time and space, reveals that He is the Creator of it all.