Mark 16

"And He said to them, “Go into all the world and preach the gospel to every creature. He who believes and is baptized will be saved; but he who does not believe will be condemned.  And these signs will follow those who believe: In My name they will cast out demons; they will speak with new tongues; they will take up serpents; and if they drink anything deadly, it will by no means hurt them; they will lay hands on the sick, and they will recover.” vv.15-18

Read chapter 16.
Have you ever compared the "great commissions" in the different gospels?  They are different and that doesn't mean that the Bible is in error but that there were multiple commissions by Jesus and each one to a specific time period and purpose.   There's a lot of focusing on the words used here to determine when this was and who this was to.  For example, today when one believes we don't see these signs follow: cast out demons, speak in tongues, not hurt by poisons, healing of sick.  Yet we do see all of these true in the book of Acts during that short 30 year time period.  The word "will" describing each one of these signs is showing a sure thing, not "possibly" or "sometimes."  A lot of confusion can happen in the first part of the commission of "all the world" and "every creature" seeming that this commission can't be fulfilled till every last person and animal (creature?) is preached to.  Yet this must be more specific and something the apostles understood as we read in Acts 11:19 that they preached "to no one but the Jews" (yes we do see some gentile believers in the Acts period, but not to them as a whole yet).  I do not believe this commission in Mark 16 is for us today but that it was completed in the period of the book of Acts (noticed the past tense used in verse 20).  Now this isn't to say then we don't need to preach the gospel because yes we should share who Jesus Christ is with all people no matter Jew or Gentile and we shouldn't want to hide that light, that joy, that hope, and most importantly salvation.  Take time to compare the different commissions in each gospel. What commission are you following in your specific life?