Summary The Pharisees conspire with the Herodians against Jesus because he heals a man's withered hand on the Sabbath. Questioning their legal and ritualistic piety, Jesus challenges them: "Is it lawful to do good or to do harm on the Sabbath, to save life or to kill?" The fame of Jesus has apparently grown because Mark next records him as being surrounded by a throng near the Sea of Galilee; because the press of the crowd is so great, he asks his disciples to take him out upon the sea in a boat. Unclean spirits fell down before him and proclaimed "You are the Son of God!"  Jesus admonished those healed not to make him known. From the sea, Jesus goes up into the mountains where he appoints the twelve:

16 So he appointed the twelve: Simon (to whom he gave the name Peter); 17 James son of Zebedee and John the brother of James (to whom he gave the name Boanerges, that is, Sons of Thunder); 18 and Andrew, and Philip, and Bartholomew, and Matthew, and Thomas, and James son of Alphaeus, and Thaddaeus, and Simon the Cananaean, 19 and Judas Iscariot, who betrayed him.

He next returns home with a crowd following him. His family describes Jesus as having gone mad; the scribes say he has been infected by Beelzebul and demons. Jesus points out to the scribes that it is illogical that he would be infected by Beelzebul at the same time that he is casting out Satan; a divided kingdom, Jesus reminds them, is a kingdom which will not stand. This section concludes with a warning about blasphemy of the Holy Spirit:

28 "Truly I tell you, people will be forgiven for their sins and whatever blasphemies they utter; 29 but whoever blasphemes against the Holy Spirit can never have forgiveness, but is guilty of an eternal sin"— 30 for they had said, "He has an unclean spirit."

This chapter concludes with word that Jesus' mother and brothers are asking for him; Jesus responds by saying that everyone gathered there are his brothers and sisters:  "Whoever does the will of God is my brother and sister and mother."

In this chapter, as everywhere in Mark, Jesus is active:

a favorite word in Mark is the Greek word meaning immediately or at once or then, which occurs about forty times in sixteen chapters. On the other hand, Mark records fewer words of Jesus than does any of the other Gospels; it contains one collection of sayings in the form of a discourse (Mark 13) and a few parables (e.g. Mark 4). Oxford Handbook

Jesus continues teaching, preaching, and healing in Galilee, and in going about his work, he continues to tangle with the religious establishment. The first controversy is over the Sabbath, with the Pharisees conspiring with the Herodians. We will recall that what is done on the Sabbath has already been an issue in the second chapter of Mark: The Pharisees observed Jesus' disciples eating corn in the fields on the Sabbath and attacked Jesus through their act.  Jesus demonstrated superior scriptural knowledge and reminded the Pharisees that David himself had suspended the rules and eaten from the bread of the Presence. Jesus clearly did not ascribe to any rules ethic where the rule always holds regardless of circumstance; he clearly sided with the act and reminded his critics that the Sabbath is for humankind, not humankind for the Sabbath. In this round, Jesus asks, "Is it lawful to do good or to do harm on the Sabbath, to save life or to kill?" His critics are silent. Jesus is clearly doing good by healing the withered hand. Jesus, acting by the principle stated in Mark 2.27, equates acts to meet human need with acts lawful . . . on the Sabbath (Oxford Annotated).

With a multitude now pressing about him, Jesus seeks solitude and distance in a boat on the Sea of Galilee. He has done the good work of healing many with diseases and unclean spirits:

"Spirit" translates words that in both Hebrew and Greek mean "wind" (Genesis 8.1; cf. Genesis 1.1) or "breath" (Genesis 6.17; Ezekiel 37.5), as well as vital essence. Biblical writers do not normally combine the two terms to designate the totality of human nature. The body/soul dichotomy that so fascinated Greek philosophy is not generally presupposed, even when the two terms occur in close proximity; thus, Matthew 26.41 is not a real exception to this rule (Oxford Companion).

The unclean spirits recognize the one casting them out as the "Son of God."  Jesus rebukes them not to make him known, reminding the reader once again that Jesus sees his mission as different from that of the expected Messiah; he is the servant walking among and healing humankind, reaching out with a gentle touch, a caring heart.

Next, Jesus appoints the twelve:

13 He went up the mountain and called to him those whom he wanted, and they came to him. 14 And he appointed twelve, whom he also named apostles, † to be with him, and to be sent out to proclaim the message, 15 and to have authority to cast out demons. 16 So he appointed the twelve: † Simon (to whom he gave the name Peter); 17 James son of Zebedee and John the brother of James (to whom he gave the name Boanerges, that is, Sons of Thunder); 18 and Andrew, and Philip, and Bartholomew, and Matthew, and Thomas, and James son of Alphaeus, and Thaddaeus, and Simon the Cananaean, 19 and Judas Iscariot, who betrayed him.

Concerning his disciples, Oxford Companion reminds us of their humanity:

The somewhat amorphous group called disciples constitutes a vital feature of all the Gospel narratives, but the authors used the term to communicate different aspects of being a follower of Jesus. In Mark the disciples are agents of instruction for the author, but as negative examples. They teach the audience or readers, but mostly through the things they do wrong or fail to understand. The constant questions and concerns of the disciples, particularly in the central section of Mark’s gospel, provide an opportunity for the author to explain the purpose of Jesus’ mission and the hidden meanings of his teaching. Discipleship in Mark involves fear, doubt, and suffering, as Mark 8.31, Mark 9.31, and Mark 10.33 make explicit; nowhere is this more poignantly captured than in the character of Simon Peter. The disciples in Mark, whomever this broad term may include, never fully understand and never quite overcome their fear and apprehensions. There is actually the hint in Mark that the disciples’ fear is in some sense the beginning of wisdom.

A question asked by Oxford Companion is significant: Did Jesus consciously act as if he were establishing the new Israel by selecting twelve representatives? The symbolic significance of the number twelve is difficult to miss.   Readers will want to look at the complete number symbolism described in the Oxford Companion; concerning twelve, it says the following:

Twelve, like seven, is a number of completeness and perfection. This number in particular must not always be taken literally. Israel always comprised more tribes than the twelve that were actually counted, and the counting of the twelve was not always uniform (Genesis 49; Joshua 13–19; Revelation 7.7–8), but the twelve meant "all Israel." It was regarded as important that there were twelve apostles and that their number should be complete, but the lists do not quite tally (See Twelve, The). The twenty-four elders (Revelation 4.4) clearly represent all Israel and the whole church. The twelve cornerstones and gates of the new Jerusalem not only link the city with the tribes of Israel and the apostles, but also signify its divine perfection, as do its measurements of 12,000 stadia square and its walls of 144 cubits. The 144,000 of Revelation 7 and Revelation 14 in each case mean that the number is complete and not one of the elect is lost; in Revelation 7 John hears the 144,000 from Israel (all Israel) being counted, but sees "a great multitude that no one could count, from every nation, from all tribes and peoples and languages" (the redeemed gentiles).

These twelve live intimately with Jesus, adopt his mission and his way of life.

In this chapter's final section, Jesus reveals the cost of his mission. His mother and brothers, concerned for his safety given the intense emotions which have been aroused around him, also begin to fear for his sanity. The Pharisees have previously recognized his powers but attributed them to Beelzebul or Satanic forces.

The Phoenician god at Ekron consulted by King Ahaziah (2 Kings 1.2–18). The name in Hebrew means "Lord of Flies," but no evidence exists for a Philistine god who either drove off flies or gave oracles through their buzzing. The Hebrew form is probably a derogatory transformation of Baal-zebul, which appears in Ugaritic texts meaning "Lord Baal," but could also be understood as "Master of the Heavenly House" (cf Matthew 10.25). In Aramaic, Beel-zebul may have been construed as "Lord of Dung," Beel-zebub possibly as "Enemy." During the Greco-Roman period, Beel-zebul came to be used for a leader among the demons opposed to God. Jesus denies that he casts out demons by authority of Beelzebul, the ruler of demons (Matthew 12.24–27 par.). Some translations employ Beelzebub in the New Testament passages, following the text of 2 Kings. Christian interpreters identified Beelzebul with Satan on the basis of the Gospel passages (Oxford Companion).

Jesus, aware of his mission to humankind as more pressing than his family's concern, replies "Who are my mother and my brothers?" 34 And looking at those who sat around him, he said, "Here are my mother and my brothers! 35 Whoever does the will of God is my brother and sister and mother."