This passage was directed to Israel not us. The gospel in Mark is the gospel of the kingdom. The promised kingdom on earth in which believing Israel will reign with Christ for a thousand years. Jesus commanded this only to the twelve........................[Mar 16:15 KJV] 15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
We dont have to be water baptized that was for Israel. Israel was water baptized for forgiveness of sins.....................
[Mar 1:4 KJV] 4 John did baptize in the wilderness, and preach the baptism of repentance for the remission of sins.
[Act 2:38 KJV] 38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
Last look at this passage.........................
[Mar 16:17-18 KJV] 17 And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues; 18 They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover.....................ALL OF THESE SIGNS MUST BE EXHIBITED IF SAVED.....................Jesus was saying those were saved by BELIEVING IN HIS NAME, Israel to have eternal life had to believe in Jesus's name, which was to believe he was Christ, the Son of God.................[Jhn 20:31 KJV] 31 But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.