I believe the Bible is God’s word because God as Lord Jesus Christ said so. There are parts that are hard to comprehend in light of the Gospel but I put my trust in the Lord by His Gospel.
Christ basically sums up the Bible by His commandments. He says in the golden rule to treat others as you would want to be treated. Read Matthew 7:12 but then backtrack & read Matthew 7:1-12. Note the Lord says that is the law & prophets ( so all of the books of the law & prophets fall within this).
The golden rule is a necessary mechanism for living but we need an absolute higher guidance for using it. Christ tells us this when He calls us to love God & neighbor ( read Matthew 22:36-40 etc.). Note the Lord says on these commandments are which the law & prophets depend ( or hang etc.). Again, we see most of what is known as the Old Testament affirmed. I will admit some accounts are difficult to say the least.
After, His resurrection, the Lord appeared to His disciples & testified further (read Luke 24:44-47). Note that the Lord has now testified to the law, prophets, & psalms ( well that is even more of the Bible).
It is by the commandments in which we know the Lord, indeed the Trinity since the Lord testifies to the Father, Son, & Holy Spirit in John 14:15-18. A rich young man was told this but got confused ( Matthew 19:16-22 etc.). St. Paul affirms the same ( Romans 13:8-10). It is in this we need our grounding or we may become confused ( not everyone but some).
The formation of the commandments begins in the Old Testament: Genesis 9, Deuteronomy 5, Deuteronomy 6, Leviticus 19 etc. Greater examples of their fruition are Psalms 15, Proverbs 14 esp. Proverbs 14:20-1, Proverbs 28, Micah 6:7-8, Zechariah 7:8-10, Zechariah 8:15-17, Ezekiel 18:4-9, Isaiah 55:6-13, Isaiah 58 etc.
These are what we do in response to what the Lord has done for us: John 3:16-21 within the way St. Paul says we are saved Ephesians 2:8-10.