The Scriptures record many instances of God and Christ speaking and acting with authority. Often, the actions backed up the words. For example, Jesus demonstrated His authority over disease in order to prove His right to forgive sins (Matthew 9:1-8).
Likewise, God prefaced the Ten Commandments by pointing out, "I am the LORD your God, who brought you out of Egypt, out of the land of slavery." I, God, have demonstrated My authority over the forces of nature and over Pharaoh to the point where Pharaoh was forced to free you from slavery. Therefore, "You shall have no other gods before Me" (Exodus 20:2-3). Freeing the people from slavery gave God the right to tell Israel what to do.
Most people who question the Bible's accuracy are really concerned to prove it has no authority in their lives. If the Scriptures are telling the truth about God and Christ, then humans have no excuse to disobey them.
-- Karen Lee-Thorp in A Compact Guide to the Bible