How can we know what God is like and what He expects of us? The truth is, if we were left to our own wisdom and reasoning capabilities, we would never arrive at true knowledge about God and how we are to worship Him. It is true that when we look at the creation around us, we know and understand (and so does the non-believer, even though he suppresses that truth) that God exists and that He is powerful (Romans 1), but we would still remain in darkness about the specific character, requirements and promises of God. Praise be to God that He has not left us in darkness, but has instead revealed Himself to us by giving us His Word, the Bible.
“Do your best to present yourself to God as one approved, a worker who has no need to be ashamed, rightly handling the word of truth.” 2 Timothy 2:15