many things contribute  to the accuracy of the bible, but the most important is the fact that the authors had to be approved according to the laws back then in terms of the type of book being written and the verification that follows that. another is archaeology.

"if the bible is the word of God, why was it written  by man?" the bible consists of words inspired from/by the Holy Spirit from God on behalf of His people. people wrote the bible because God chose for it to be that way. If God wanted to make the bible appear on it's own with no help He could've done that, but He didn't. and it's funny because although God used people to record history, the bible doesn't need people to affect people. If someone were to pick up a bible and read it, the Holy Spirit can come upon them from that alone because God's word is alive, it's just recorded on paper. God doesn't need preachers, teachers, evangelists or even historians, but He chose to use them for the sake of witness and for His glory.

the bible contains commandments but it's not a rule book. it's a guidance book. it's holy and derived from the Holy Spirit. everything written in it is to keep us in right standing in our relationship with God and to guide us along the way. also, because the word is alive, the scriptures are an active tool to use against the schemes of the enemy, just as Jesus did when He was tested by satan himself. it's not meant to replace your relationship with your Heavenly Father, but to remind you of what He has already spoken and says about whatever you're dealing with. He always has a fresh revelation for His children.