A case can be made both for and against these verses. A majority of the Greek manuscripts of the New Testament do include them – going back to the earlier half of the second century – and so they were included without note in the King James Version and many other older English translations. But the text of verses 9-20 is not found in the very earliest known Greek manuscripts, and the early Christian scholars Eusebius (c. AD 260-339) and Jerome (c. AD 347-420) both state that the verses were not present in the best manuscripts of Mark that they could find.
How are we to decide, then, whether the verses “belong” in the Bible or not? Perhaps the best approach is to look carefully at what they say and to try to decide on that internal evidence. First, verses 9-20 do not flow naturally after Mark 16:8 – there is a noticeable disconnect in what is said. Although the subject of verse 8 is “the women,” the subject of verse 9 suddenly changes to Jesus, and there is some unnatural repetition. Verse 9 states “… early on the first day of the week…” while verse 2 has already told us “Very early on the first day of the week …” Verse 9 also mentions somewhat repetitively “Mary Magdalene out of whom he had driven seven demons,” when Mary Magdalene was already introduced to the reader in verse 1 of chapter 16.
So verses 9-20 give several indications of a rather awkward summary of the resurrection that was added after Mark was written. This may have occurred because with verse 8 the Gospel of Mark ends rather abruptly. It is possible that Mark did not get to finish the Gospel he was writing, though the abrupt ending of verse 8 is actually in keeping with the style of the Gospel and the way Mark often handles his material. But it is easy to see why some early Christians may have wanted to “round out” the ending and bring it more into line with the endings of the other Gospels.
In fact, that is an important point to remember. The material in Mark 16:9-20 is essentially found in the endings of the other three Gospels. So if we do feel these verses are additional to what Mark originally wrote, we are not rejecting any of the material they contain that is found in the other accounts of Jesus’ life. On the other hand, the basic principle of never deciding doctrine or important beliefs based on passages of Scripture that are of uncertain origin or meaning still holds.
We should also remember that there is variation in many of the early manuscripts of the New Testament. There are even a few cases of other endings to Mark’s Gospel. Ultimately, our faith in the inspiration of the Bible depends not on a particular manuscript, but on the guidance God has given in the process of preserving his word. Often, as in the ending of Mark, even when there are uncertainties we are able to come to an understanding of what the original text likely was.