Can we really know that the Bible is true and allow it to guide us?   

Over the centuries, there have been many archaeological discoveries that support various events in the Bible - ie the discovery of the legendary city of Jericho, the discovery of the ancient Hittite nation in the modern country of Turkey, an Assyrian King named Sargon was discovered in writings found in modern Iraq, etc...  There are many others that are well documented.  The fact remains that no archaeological discovery has yet to contradict any Bible story.

Another way one can know the Bible is true is due to the historical references that are found to be accurate.  Many prophesies and actual accounts exist in the Bible that support real world events - ie the fall of the Assyrian empire, the fall of the Babylonian empire, the demise of Israel as a nation, etc... Many of these prophesies were written hundreds of years prior to the actual event taking place.

Finally, there are many teachings in the Bible that are the cornerstone of morals in many societies throughout the centuries - one should not commit adultery, one should not steal, one should not lie, one should not kill etc... All of these teachings can be summed up by the one taught by our Lord and Savior - "Love your neighbor as yourself". Of course, the most important commandment was this - "Love the Lord your God with all your heart, soul, mind, and strength!" Doing these things requires knowing that God is a rewarder of those who diligently seek him.  In order to seek Him one must study God's word (The Bible) and submit to his word by obedience to His Commands!  By sincerely studying His Words and submitting to them, one will learn the Bible is true!