In Mark 15:21–39 we come to the crucifixion of Jesus Christ. Suffering and death is part of what Jesus came to do (Mark 8:31). He does so in order to free God’s people from the penalty of sin (Mark 10:45). Jesus’ crucifixion will also be the moment where someone finally confesses that Jesus is the Son of God.
In Mark 1:1 we were told that the Gospel is about Jesus the Christ, the Son of God. The first time that someone realized the identity of Jesus was in Mark 8:29, when Peter confessed that he is the Christ. This confession did not, however, include the fact that Jesus is the Son of God. With the confession of the Roman centurion (Mark 15:39), Jesus is recognized to be the Son of God, as also testified by the Father with his baptism and transfiguration (Mark 1:1, Mark 9:7), acknowledged before the Jewish leaders (Mark 14:61–62), and confessed by demons (Mark 1:24; Mark 3:11; Mark 5:7).1
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.