I totally question this longer ending of Mark. If there is an ending to Mark, it was lost in antiquity, and I assume God wanted it that way. Perhaps being at the end of a scroll, the ending fell into tatters, and was not copied before the original manuscript was lost.
Suffice it to say that both the historical and textual evidence point to the fact that both the longer (the used in the OP) and the shorter ending are simply not the words of Mark.
Historically, we can look at the manuscript evidence. The extant manscripts date from 135 AD at the earliest to about 1200 AD for the latest. There are 5000 copies of the New Testament, which range fromm scraps and pieces (Rylands papyrus of John, for example) to complete manuscripts. These texts show remarkable agreement among themselves. The most notorious exception to this happy rule is the ending of Mark.
The oldest and most important manuscripts of the Bible, codex Vaticanus and codex Sinaiticus omit verses 9-20, as do several early translations or versions, including Old Latin, the Sinanitic Syriac, about 100 Armenian manuscripts and the two oldest Georgian manuscripts.
Neither Clement of Alexandria nor Origen shows any awareness of the longer ending, and Eusebius and Jerome attest that vv 9-20 were absent from the majority of Greek texts. Although there are a few manscripts which do include this ending, attesting to the fact that it was added quite early and included in subsequent copies of Mark, even those copies include scribal notes or various markings indicating that the ending is regarded as a spurious addition to the gospel.
Thus, external evidence (manuscript witnesses) argue strongly against the originality of the longer ending.
Literary or textual criticism also points to the ending not being original. The text changes abruptly from the fear of the women, to "Lord Jesus" a term not used by Mark, who calls Jesus by his given name in the rest of the book. Such reverential nomenclature likely derives from later Christian worship.
Particularly noticable is the newcomer introduced in this ending, as well as the words that appear nowhere else in Mark. In the shorter ending, nine of the thirty-four words are new. In the longer ending there are an additional 18 words that do not otherwise appear in Mark, plus several unique word forms, and syntactical constructions.
Several of Mark's signature stylistc features are absent in the longer ending. Most notably, the absence of the initial Greek "
kai" (and also, even) in Mark's sentence structure and the absence of the historic present tense of verbs and the absence of the word
"euthys" (immediately, forthwith
).
Greek Concordance: εὐθὺς (euthys) -- 51 Occurrences
Finally, the longer ending also includes themes peculiar to itself, some of which contradict Markan themes. For example, the repeated chastisement of the disciples for their "unbelief" of the gospel proclamation, is unique to the longer ending, and the prominence given to charismatic signs in vv 17-18 stands in stark contrast to the reserve of Jesus in Mark with regard to sign and sensation (see 8:11-13)
"
11 The Pharisees came and began to argue with him, seeking from him a sign from heaven to test him.12 And he sighed deeply in his spirit and said, “Why does this generation seek a sign? Truly, I say to you, no sign will be given to this generation.”13 And he left them, got into the boat again, and went to the other side." Mark 8:11-13
External and internal evidence gives the conclusion that 16:9-20 is not the original ending of Mark but rather a later addition to the gospel. The longer ending is old, perhaps dating to the end of the second century, but it is not the original and should NOT be used for doctrine, or forming a church (eg: The Shakers!)