Acts 9:1-22; Ps 117(116):1. 2; Mark 16:15-18
The end of Marks Gospel is missing - so to is the beginning, as the Mark we have starts with Jesus's baptism, not his birth! Now, these early gospels were assembled into codex - what we would now call a book - rather than a scroll. So it is entirely possible that the first sheet of paper or two from the original written word got lost before the time that copies began to be made!
At some point a different author (the linguistic style is rather different) added a more rounded ending to Mark, which had ended with the disciples leaving the tomb in confusion and dismay, lost both in the crucifixion and now in the disappearance of Jesus's body. Todays reading is from that extension and tell the disciples to go out and spread the good news - which indeed they did, as every one of the instructions here, are carried out in the Acts of Apostles.