Scripture is about God and His glory, and we can trust its inerrant revelation about Him precisely because He is without error and has inspired the Scriptures.
The physical act of writing out letters and then physically sending them in the mail to others is part of a bygone era. These days, fingers strike digital keyboards and send icons, and digital texts and emails are electronically sent. But while the format of writing and sending letters has largely changed in our digital age, two things have remained the same: Who writes the letter and what they have to say still matters a great deal.
We largely care about the content of letters because of who has sent them. If I were to receive a certified letter from the President of the United States and, within this letter, he was to present me with an invitation to the White House, wherein I was to be honored with a reward, I would pay special attention to every word written. As one in a position of authority and power, his words in such a letter would carry significance and weight. On the other hand, when I receive an email from the latest displaced Nigerian prince requesting I give him full access to my bank account, I give much less weight to what is written. The former writes from a position of power and authority; the latter writes with no authority.
The biblical doctrine of inerrancy has just as much to do with who has inspired the Scriptures as it does with what the inspired Scriptures have to say. If, for example, we were to contend that the Scriptures had been inspired by a mere mortal man, then we would place much less significance on what they have to say. Even if the man purported to have inspired them was generally acknowledged as good, trustworthy, and mostly faithful to the truth, we would still have to consider it likely that he had gotten certain facts wrong. We would even need to agree that his directions and commandments could be the result of his own faulty desires, and therefore not always good. We could hardly claim a book inspired by a mere mortal man was inerrant; on the contrary, we would be forced to admit that it was extraordinarily likely that there were multiple errors and inconsistencies to be found throughout.