This passage is part of the third and final section of Mark’s Gospel.
In this final section, Jesus no longer avoids the crowds or maintains secrecy. He teaches publicly in the temple where everyone can see him and where he is confronted with opponents (Mark 11:1 – 12:44). Those who dislike Jesus are jealous of his popularity and wish to have him killed (Mark 11:18; Mark 12:7; Mark 14:1). After spending time in the temple, Jesus then moves to the Mount of Olives, where he predicts the destruction of the temple and then gives his disciples instructions on what to do during the time leading up to its destruction and how it relates to the return of Christ (Mark 13:1–37).
21 And they compelled a passerby, Simon of Cyrene, who was coming in from the country, the father of Alexander and Rufus, to carry his cross.