Expositor's Bible Commentary Commentary Mark 3:15

"and to have authority to cast out demons:" — Mark 3:15 (ASV)

The purpose for which the Twelve were appointed was twofold: (1) they were to be brought into close association with the Son of God, live with him, travel with him, converse with him, and learn from him; (2) the training was not an end in itself—they were to be sent out to preach the Good News and to drive out demons. These last two elements are closely associated. The salvation Jesus brings involves the defeat of Satan and his demons.