Hummmmmm.
Mark 16:15-16: "And he said unto them, Go ye into all the world, and preach the gospel to every creature. He that believeth and is baptized shall be saved; but he that believeth not shall be damned."
This passage may be dispensed, in my view, without discussion of baptism. The evidence is strongly against its inclusion (and that of Mark 16:9-20 as a whole) in the text:
External evidence. The two earliest parchment codies, Vaticanus B and Sinaiticus, plus 2 minuscules and several versions and manuscripts, do not contain verses 9-20. Two important early Christian writers testify that these verses are not found in Mark: Eusebius (Quaestiones ad Marinum I) says that they are not in "accurate" copies of Mark and are missing from "almost all" manuscripts; Jerome (Epistle CXX.3, ad Hedibiam) testifies that almost all Greek manuscripts of his time lack vss. 9-20.
Many manuscripts that do have these verses "have scholia stating that older Greek copies lack them," and other textual witnesses add "conventional signs used by scribes to mark off a spurious addition to a literary text." There are also several variant endings of Mark in circulation. Our vss. 9-20 are the most common, but there is also a "short" ending, and seven Greek manuscripts with both the long and short ending.
Internal evidence. There is a sudden change in subject from verse 8 (the women) to verse 9 (Jesus). Mary Magdelene is introduced as one from whom Jesus had cast out seven demons, as though she had not been introduced in the Gospel before. The form, language, and style "militate against Marcan authorship."
There are seventeen non-Marcan words or Marcan words used in a non-Marcan sense. There is no instance of the typical Marcan stylistic transitions or methods (such as beginning a phrase with a parataxis). Overall, the passage has the "distinct flavour of the second century" and appears to be a pastiche of material taken from other Gospels. [See for this data Markan commentaries by Brooks (272-3), Lane (601-4), and Anderson (358).] ~ JPH (literature specialist)
Well, the statement itself is provable(true) from other sources. Matthew directs us to preach the gospel(Mat 28:19). Belief is addressed in Luke 8:12.(though logically it would take more to derive the last statement in Mark 16:16) IOW If A and B then C does not directly implicate if not A then not C nor does If A then C directly implicate if not A then not C. But of course, If C then A does imply if not A then not C since it is the contrapositive.(If you are saved then you believe)