We study the Bible, very simply, because God tells us to: "Do your best to present yourself to God as one approved, a worker who does not need to be ashamed and who correctly handles the word of truth." 2 Timothy 2:15
Christianity is based in reality and truth.
These are revealed in the Bible.
The Bible is God's Word and equips the believer for life.
"All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work." 2 Timothy 3:16-17 (NIV)
The scriptures have been deposited into the church for safe keeping for men of this time.
Paul tells Timothy (and the rest of us) to guard the good deposit:
"What you heard form me, keep as the pattern of sound teaching, with faith and love in Christ Jesus. Guard the good deposit that was entrusted to you-Guard it with the help of the Holy Spirit who lives in us.” (1 Tm.1:13,14)
If we lose the truth, we lose the sphere of reality we are to operate in as believers. We will then lose Christianity.
Peter tells us: “There were also false prophets among the people, just as there will be false teachers among you. They will secretly introduce destructive heresies." (or, “deviations to the truth) 2 Peter 2:1
If you do not study the Bible you will end up with a religion like the Samaritans had. Jesus said to them:
“You Samaritans worship what you do not know; we worship what we do know, for salvation is from the Jews.”