We don’t know for sure what Jesus’ final words were in the Gospel of Mark. The closing verses of the book, Mark 16:9-20, are in doubt as to their authenticity. The Bible Knowledge Commentary tells us,
The external evidence includes the following: (1) The two earliest (fourth century) uncial manuscripts (Sinaiticus and Vaticanus) omit the verses though their respective scribes left some blank space after verse 8, suggesting that they knew of a longer ending but did not have it in the manuscript they were copying. (2) Most all other manuscripts (fifth century on) as well as early versions support the inclusion of verses 9-20. (3) Several later manuscripts (seventh century on) and versions supply a “shorter ending” after verse 8 which is clearly not genuine but all these manuscripts (except one) continue on with verses 9-20. (4) Early patristic writers—such as Justin Martyr (Apology 1. 45, ca. A.D. 148), Tatian (Diatessaron, ca. A.D. 170), and Irenaeus who quoted verse 19 (Against Heresies 3. 10. 6)—support the inclusion of these verses. However, Eusebius (Questions to Marinus 1, ca. A.D. 325) and Jerome (Epistle 120. 3; ad Hedibiam, ca. A.D. 407) said verses 9-20 were missing from Greek manuscripts known to them. (5) An Armenian manuscript of the 10th century attributed verses 9-20 to “the presbyter Ariston,” probably Aristion, a contemporary of Papias (A.D. 60-130) who was purportedly a disciple of the Apostle John. (6) If Mark ended abruptly at verse 8, then it is easy to see why some early copyist(s) wanted to provide a “suitable” ending for the Gospel from other authoritative sources. However, if verses 9-20 were part of the original, it is difficult to see why the early copyists would have omitted it.
Skeptics often cite this passage as evidence of the Bible’s unreliability. I can still remember, however, my very first Bible given to me by my church in grade school, and its marginal note cautioning that this passage was in doubt. The same with the John 7:53-8:11, whose authenticity is even less likely than this passage’s.
Bible scholars and publishers are honest about textual issues. A good study Bible’s margins are peppered with possible variants. And not one of them affects a single point of history or doctrine.
This Marcan passage comes as close to an exception on that as any, where it says that those who follow Christ will “pick up serpents with their hands, and if they drink any deadly poison it will not hurt them.” We know from Church history that snake-handling and poison-drinking never became an accepted practice of the church, which indicates that from the start, no one thought this was a normative instruction.
I am aware of three possibilities for explaining this passage. Either (1) the text is inauthentic in the first place; or (2) this is a figurative way of saying that God would be with his followers and protect them from various harms; or (3) since these were named as part of a list of “signs,” they were expected to happen only rarely, as is the case other signs recorded in the Bible and history.
Option 1 is certainly possible. Option 2 is unsatisfactory to me: there are too many exceptions. Option 3 makes sense. We do know of a case where Paul survived a snake bite (Acts 28:1-6), and had to explain to the witnesses that he was not a god.
I should also mention another potential controversy in Mark 16:16, where Jesus almost makes it sound like baptism is essential for salvation. Few Protestant churches believe this is to be the case. It seems to me that the latter portion of that verse is enough to show that Jesus didn’t intend that, since he did not say, “whoever does not believe or fails to be baptized is condemned.”
I hold to a generally Baptist view: baptism was and still is a public statement of belief; it is the way a new believer enters into the company of the faith. For that reason alone (there are others, I am not presenting a full theology of baptism here) it is vital to any believer’s walk with Christ. It is essential, even if not for salvation.
The rest of this disputed passage is echoed in Matthew and Luke, so that what it says is attested well enough elsewhere that there’s no need to wonder about it here.