The alternative, longer, ending to Mark mentions the Ascension of Jesus and then states that the disciples went out and proclaimed the good news. Their words were accompanied by confirmatory signs sent by God. I wonder in what ways we go out and proclaim the good news. I wonder what we have to say about God. I wonder to what, if anything, we point as indicative of God at work.
The critical point is that the story goes on. I wonder how we see it continuing in our day. I wonder what we do to tell it. This is the sheer wonder of gospel, that God participates with us. Whoever wrote this was not trying to eliminate the questions that we might see as being left at the end of verse 8, but is expressing confidence in the continuing presence of Jesus and of the story moving forward as his followers do his work and tell his good news, As Bonnie Bowman Thurston (Preaching Mark) says – “The reality of the risen Jesus and his continued involvement with his disciples provides both continuity with the resurrection account in v. 1-8 and a word of hope for today’s disciples, The Gospel continues to spread and the Lord continues to work with us (v. 20), and that is very good news indeed.”