Mark 16:15-18 (ESV)
And he said to them, "Go into all the world and proclaim the gospel to the whole creation.  Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.  And these signs will accompany those who believe: in my name they will cast out demons; they will speak in new tongues;  they will pick up serpents with their hands; and if they drink any deadly poison, it will not hurt them; they will lay their hands on the sick, and they will recover."
You might think 17 and 18 are the most controversial of the verses here recorded. But they are easily dealt with. The disciples in their life time did cast out demons, they spoke in tongues (Pentecost, as well as elsewhere, where they were understood, none of this Pentecostal bs.) Paul was bitten by a serpent and lived, many recovered from illness.
The more controversial verse is 16. “Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.’ It’s controversial because people refuse to believe it. they want to believe anything but what it says. Baptists think because the second half of the verse doesn’t mention baptism, that somehow this negates what the first half says about baptism. This verse makes baptism necessary. Very necessary. Belief and baptism go together. One cannot believe and refuse to be baptized. God makes promises in baptism a believer wants. In fact the way the words work here the two are almost synonymous. If you believe you will be baptized. If you don’t believe you will not be baptized. This is why the second part doesn’t mention baptism, it would be redundant to say if you aren’t baptized, that is a given because you don’t believe.
What would it mean if it said “who ever believes and is baptized will be saved, but whoever does not believe and is not baptized will be condemned.” How would that add anything to what was said? It would actually change things a little bit though, wouldn’t it? Then some would say, well he didn’t believe but he was baptized…. Baptism does nothing without faith. Lutheran’s believe that. If one loses faith, he rejects his baptism. It isn’t that the baptism is nothing in and of itself, but a person refusing to believe negates the gifts baptism gives. Should one return to the faith though, they latch hold of those promises given in faith. For this reason faith and baptism go together in this verse, and it isn’t mentioned a second time in conjunction with unbelief.