Faith is closely connected with healing in Mark. Jesus heals the paralytic on the basis of the faith of his friends (and of the paralytic himself, too?) in 2:5. Mark 5:34, 7:29, 10:52 feature similar healings where the faith of the healed seems to be at least a partial basis for Jesus’ healing.
At the same time, Jesus shows his frustration with lack of faith. He exhorts his disciples in 4:40 after he calms the storm, since they are afraid and not showing faith. In 6:6 and 9:19 Jesus expresses disapproval of the crowd who does not have faith in him. And in Mark 11:22 Jesus tells the disciples, “Have faith in God” (or, “Have the faith of God,” ἔχετε πίστιν θεοῦ).
Causation in general is difficult to prove, and although some hold that Mark 6:5-6 say that lack of faith limits Jesus’ power, one should be careful not to conclude from Mark that if someone is physically sick or mentally ill, it is just because that person does not have enough faith. At the same time it is clear that in Mark Jesus heals those who have faith. Mark seems to convey that Jesus’ act of healing is at least in some sense related to their faith, if not a direct result of it.
Robert A. Guelich, in his commentary on Mark, writes, “Faith represented the critical link in one’s relationship with Jesus” (312-3). And, “although Mark does not actually define ‘faith,’…it meant much more than being impressed with Jesus’ words and deeds in view of his modest family background. …To those who came to him in faith seeking help…, he responded by meeting their need” (313).
Just as Jesus tells the disciples (as noted above) to “have faith,” he says in Mark 9:23, “All things are possible for the one who believes.” The father of the boy with an evil spirit says, “I believe (πιστεύω), help my unbelief (ἀπιστία)!”
Mark’s Gospel finally reaches a Christological culmination in the profound profession of faith by the centurion in chapter 15, who declares Jesus to be truly the “Son of God.” Such faith!