“He who believes and is baptized will be saved.” Mark 16:16 is the only verse in the New Testament that clearly says a person has to be baptized to be saved. Although some people say verses such as Acts 2:38, “repent and be baptized,” say the same thing, that is not actually the case. Acts 2:38 is simply saying if a person did repent and get baptized he would receive the holy spirit, which is true, but different from saying one had to do those things to get the holy spirit.
Salvation is the most serious subject in the Bible, and thus this verse requires our attention. However, studying it in light of the scope of the New Testament, it seems unreasonable that water baptism is necessary for salvation, but it is only mentioned here and not in any of the other clear verses about salvation. For example, Romans 10:9 says very clearly: “That if you confess with your mouth, ‘Jesus is Lord,’ and believe in your heart that God raised him from the dead, you will be saved.” That fact, along with all the evidence that the closing section of Mark is not original, is very solid evidence that this verse is not original, but was added, and that makes sense because as Christianity developed in the decades after Christ’s ascension, the doctrine that water baptism was necessary for salvation became a part of Church doctrine, even though it had never been a doctrine before then.
If someone did want to insist that Mark 16:16 is original and a person had to be “baptized” to be saved, then the “baptism” in the verse would not refer to baptism in water but to baptism in holy spirit. In that case, the statement “Whoever believes and is baptized [in holy spirit] will be saved” would be true, because at the time a person believes, he is baptized in holy spirit, and then his salvation is assured. See commentary on Mark 16:9.