The doctrine of inspiration is not compromised if God chose to use more than one inspired writer for a book. Let's not be unbelieving believers. Most Bibles point out this possibility. The reason for this textual question is that some of the manuscripts of Mark do not contain these verses.
Manuscripts are hand-written copies of Scripture before the invention of the printing press.
We have no originals, but there are over 5,000 New Testament manu- scripts in the Greek language alone. Perhaps the most cogent argument is the literary style in these latter verses differs from the rest of the gospel. The verses in question may have been written at a later date by another inspired writer. It holds that God superintended the writers and the writings of Scripture so that the whole Bible is the word of God, right down to the very words used in the original. See the next answer for an example of misuse of broad conclusions.