We Know God's Truth through God's Word
If I discover truth from the Bible, how do I know the Bible is true? External evidence proves the Bible is reliable. There are 5,366 copies of the Bible dating from the time it was written to just 70 years afterwards. That dispels the urban legend that the Bible was changed as it passed through generations and languages. External evidence also includes many archeological discoveries. Historians used to say that Solomon couldn't have had the horses the Bible says he had but then thousands of horse stables were found in an archeological dig. There's also the internal evidence of the Bible itself. In a court of law, a prosecutor with one or two eyewitness accounts has a good chance of making his case. The Bible is filled with eyewitness accounts. Moses was there when the Red Sea split; Joshua was there to watch Jericho fall; the disciples saw the resurrected Jesus. The internal evidence also includes the fact that the Bible tells one story with consistency though it was written over 1,500 years on three different continents by 40 different authors from every walk of life. No human being could account for that. It's an amazing example of God's abilities.
“All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness,”
II Timothy 3:16 NKJV