What does Mark 6:7 mean?By separating the Twelve into groups of two, Jesus follows the Old Testament law of affirming the truth with two witnesses (Numbers 35:30; Deuteronomy 17:6). This idea of confirmation is also recommended in the New Testament (2 Corinthians 13:1; 1 Timothy 5:19). Going on missions in pairs provides encouragement, affirmation, and safety (Mark 11:1; Luke 7:18–19; Acts 8:14; 9:38; 11:30).
Matthew's account includes much more detail, particularly what Jesus teaches the Twelve in preparation for their trip (Matthew 10). Jesus intends the Twelve to be extensions of Himself, reaching the "sheep without a shepherd" (Matthew 9:36). The authority He gives them includes healing, raising the dead, cleansing lepers, and casting out demons (Matthew 10:8). Jesus warns them about coming persecution and exhorts them to reject fear and stay on mission. He tells them that although the gospel brings life, it also separates those who accept it from those who don't.
The authority the Twelve have over demons isn't absolute. In Mark 9:14–29, they will be unable to exorcise a demon from a little boy, despite their successes in this earlier experience. Likewise, this authority isn't exclusive. Although the Twelve are specifically charged by Jesus, others who have faith in Him will receive similar abilities (Mark 9:38–41).
This commission is an example of an important cultural custom from the Biblical era. Then, a servant sent on an errand had the same authority as the master who sent him. This gives insight into the seeming contradiction in the story of the healing of centurion's servant. In Matthew 8:5–9, a centurion approaches Jesus and explains that his servant is paralyzed and he knows that Jesus can heal him with a mere word. Luke 7:2–8 indicates that the centurion sent Jewish elders to explain his servant was sick and friends to say he believed Jesus could heal with a word. This is not a contradiction. It merely shows that the centurion sent the elders and his friends in his name with his authority. Likewise, the Twelve represent Jesus. When they speak Jesus' message, it's true that Jesus is speaking to those listeners.