Why do Christians live their lives according to a book? The main reason we live our lives by the instructions from a book is we believe four things the Bible claims about itself.
1. The Bible claims to be the actual words of God.
All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: 2 Timothy 3:16
For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost. 2 Peter 1:21
Christians accept this claim as true.
For this cause also thank we God without ceasing, because, when ye received the word of God which ye heard of us, ye received it not as the word of men, but as it is in truth, the word of God ,which effectually worketh also in you that believe. 1 Thessalonians 2:13
Christians believe that God Himself is the very author of the Bible. The words of Scripture were dictated by God to human writers. Therefore, we must obey and live by every written word in the Bible.