Complete the following sentence: The Bible was written by [_______]
To an atheist, the answer is often something along the lines of "bronze age goat herders". At the very least, their answer is always man. Faithful Christians, however, understand that these men were not just writing their own opinions. The Bible is not just man's best guess, but rather, it is the very word of God.
How surprising is it, then, that many who call themselves Christians align themselves more with the atheist view? They believe in God, yet to them, the Bible was still written by primitives with little to no education, and no guidance from the divine. The Bible really is, in their minds, man's best guess.
Here's the major problem for such people: If the Bible is, in fact, not inspired by God, then there is no authoritative source of Christian doctrine! Not only is the Bible only man's best guess, but whatever doctrines they believe are, by the same token, just man's best guess. But if this is the case, their religion becomes less about following God and more about inventing a god to follow them.
The Biblical God does not leave us with such uncertainty. Those who deny the inspiration of the Bible must deny a lot more than just its inspiration. They have to deny the very authority of Christ, who we know professed the truth of the Scriptures so vehemently that He appealed to them to prove His own authority.
If you claim to be a Christian, the inerrancy of Scripture is not a mere option, it's mandatory. You don't get to pick and choose when God spoke and when a human author just decided to take a shot in the dark. Believe and obey the scriptures as faithfully as if they were penned and delivered to you by the very hand of God. Because effectively, they are.