'Get behind me, Satan!' (Mark 8:33)
'Teacher, we saw someone casting out demons in your name, and we tried to stop him, because he was not following us.' But Jesus said, 'Do not stop him.' (Mark 9:38-39)
Even the chief apostle, the one on whom Jesus founded the church, is capable of falling into patterns of thinking that align with Satan rather than God (Mark 8). Yet shortly later, the disciples are concerned that strangers are casting out demons in Jesus’ name (Mark 9).
In Mark 8 we learn that the work of Satan can be done by those close to Jesus. In Mark 9 we learn that the work of God can be done by those far from Jesus.