What is the purpose of the abrupt ending of Mark 16?  That is discovered by considering what the desired response would have been to the angel’s commands. The correct response would have been faith in the words taught by Christ regarding his death and resurrection and then a hastened obedience in reporting to the disciples what they had seen and heard.  However, in the place of faith and obedience was amazement and fear.  This has been the dominant theme in the gospel of Mark.  Other than a few exceptions, the responses to Jesus’ teachings and miracles were amazement and fear instead of faith and obedience.  It has been well said that the gospel of John contains rich and prevalent teachings about true belief, but the gospel of Mark certainly highlights the necessity of faith.
Moreover, it has been clear in Mark that unbelief always leads to disobedience and think about what failed to happen to these witnesses of the empty tomb in light of how often Christians get caught up in trying to prove Christ’s resurrection with evidences and extra-biblical history.  Those things can serve a purpose in bolstering a Christian’s faith, but those things will never bring about saving faith in an unbeliever.  Only a Spirit-granted belief in God’s word can produce salvation and sanctification.