Sorry I am so late to the thread. A busy day for me! Outside, family visiting, and so forth.
The reason that it is important to decide which texts are original and inspired and which are spurious, is because it is very dangerous to make doctrine on a text which is not in the originals. Witness the discussion between OH and HRFTD! Not sure where I stand with that scripture either.
My two big spurious texts are the longer ending of Mark 16, and the woman caught in adultery, in John 8. But, the longer ending of Mark bothers me more, because the doctrine is just so wrong!
So, here are the reasons I do not think the longer ending Mark is original, inspired Scripture.
The 2 oldest and most important manuscripts for the NT, Codex Vaticanus (B) and codex Sinaiticus (א) omit 16:9-20 as do several early translations or versions, including Old Latin, the Sinaitic Syriac manuscript, about 100 Armenian manuscripts, and the 2 oldest Georgian manuscripts.
Neither Clement of Alexandria nor Origen shows any awareness of the existence of the longer ending and Eusebius and Jerome attest that vv 9-20 were absent from the majority of Greek copies of Mark known to them.
Although a majority of ancient witnesses, including Greek uncial and minuscule manuscripts, church fathers, this does not compensate for the textual evidence against them. The inclusion of vv 9-20 in many manuscripts is accounted for by the fact that the longer ending, which must have been added quite early, was naturally included in subsequent copies of the gospel. Many of ancient manuscripts that do contain the longer ending, however, indicate by scribal notes or various markings that the ending is regarded as a spurious addition to the Gospel. External evidence (manuscript evidence) thus argues strongly against the originality of the longer ending.
The secondary nature of the longer ending is further corroborated by the application the techniques of literary criticism. This is apparent from the first verse of the longer ending, which is a conspicuous non-sequitur; whereas the subjects of v 8 is the frightened and fleeing women, v 9 begins by supposing the resurrected Jesus, who appears to Mary Magdalene. The latter, is introduced as a newcomer "out of whom [Jesus] had driven 7 demons" although Mark has mentioned her 3 times immediately before (15:40, 47; 16:1). In vv 9-20. Jesus is for the first time in Mark referred to as "Lord Jesus" (v 19) or simply "the Lord" (v 20) rather than Mark's custom of calling Jesus by his given name. Such reverential nomenclature likely derives from later Christian worship.
Particularly noticeable is the number of new words that appear nowhere else in Mark. In the so-called shorter ending of Mark, 9 of the 34 words are new. In the longer ending there are an additional 18 words that do not appear in Mark, plus several unique word forms and syntactical constructions. Several of Mark's signature stylistic features are likewise absent from the longer ending. The longer ending also includes themes peculiar to itself, some of which contradict Markian themes. The repeated chastisement of the disciples for their "disbelief" 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 signs and sensation. (8:11-13)
External and internal evidence thus necessitates 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 a patchwork of resurrection appearances (or summaries) taken from the other three gospels, the chief theme of which was the disbelieve of the disciples (vv 11, 13, 14, and 16). Although the longer ending is clearly secondary, it is nevertheless very old.
Excerpted from The Gospel According to Mark (The Pillar NT Commentary) by James R.Edwards Pgs 497-499. A list of added words is available if requested.
So, in my opinion, God for some reason, allowed the real ending, written by Mark to be lost. However, it was various scribes who added this longer ending. It is simply not wise to make any doctrine or draw any conclusions from this spurious portion of Scripture.