Jesus contends with the Pharisees over keeping the Sabbath and they accuse him of casting out demons by the power of demons. Some very well known statements of Jesus are in this chapter, concluding with “those who do the will of my Father in heaven is my brother, and sister, and mother.”

Matthew 12

At that time Jesus went through the grain fields on the Sabbath day. His disciples were hungry and began to pluck the heads of grain and to eat.

2 When the Pharisees saw it, they said to him “Look, your disciples do what is not lawful to do on the Sabbath day.”

3 But he said to them “Have you not read what David did, when he and those with him were hungry? 

4 How he entered into the house of God and ate the showbread, which was not lawful for him to eat, nor for them which were with him, but only for the priests?

5 Or have you not read in the law, how that on the Sabbath days the priests in the temple profane the Sabbath, and are blameless?

6 But I say to you that in this place is one greater than the temple.

7 If you had known what this means: ‘I desire mercy and not sacrifice,’ you would not have condemned the innocent.

8 For the Son of man is Lord of the Sabbath.”

9 When he departed that place he went into their synagogue.

10 There was a man with a withered hand. And they asked him “Is it lawful to heal on the Sabbath?” so they might accuse him.

11 He said to them “What man among you, if he has one sheep, and if it falls into a pit on the Sabbath day, would not take hold of it and lift it out?

12 How much better is a man than a sheep? So it is lawful to do good on the Sabbath.”

13 Then he said to the man “Stretch out your hand.” He stretched it out and it was restored, as good as the other.

14 Then the Pharisees went out, and held a council against him, how they might destroy him.

15 But when Jesus knew it, he withdrew from there: and great crowds followed him and he healed them all;

16 And warned them not to make him known:

17 That it might be fulfilled which was spoken by Isaiah the prophet, saying,

18 “Behold my servant, whom I have chosen; my beloved, in whom my soul is well pleased: I will put my spirit on him, and he shall show judgment to the nations.

19 He shall not argue or shout; neither shall any man hear his voice in the streets.

20 He will not break a bruised reed, nor put out a smoldering wick, until he leads justice to victory.

21 And in his name the nations will hope.”

22 Then they brought one possessed with a demon to him, blind and mute: and he healed him so that the man could both see and speak.

23 All the people were amazed, and said “Is not this the son of David?”

24 But when the Pharisees heard it, they said “It is by Beelzebub the prince of demons that he casts out demons.” 

25 Knowing their thoughts Jesus said to them “Every kingdom divided against itself is brought to desolation; and every city or house divided against itself shall not stand:

26 And if Satan casts out Satan, he is divided against himself; how shall then his kingdom stand?

27 If I by Beelzebub cast out demons, by whom do your children cast them out? Therefore they shall be your judges.

28 But if I cast out demons by the Spirit of God, then the kingdom of God has come upon you.

29 How can one enter into a strong man’s house, and steal his goods, without first tying up the strong man? Then he can steal from his house.

30 He that is not with me is against me; and he that does not gather with me scatters abroad.

31 So then I tell you All manner of sin and blasphemy will be forgiven; but blasphemy against the Holy Spirit will not be forgiven.

32 And whoever speaks a word against the Son of Man will be forgiven; but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come. 

33 Either make the tree good and its fruit good; or else make the tree bad and its fruit bad: for the tree is known by its fruit.

34 Brood of vipers! How can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks.

35 A good man out of the good treasure of the heart brings forth good things: and an evil man out of the evil treasure brings forth evil things.

36 But I say to you, every idle word that people speak, they shall give account for it on the day of judgement. 

37 For by your words you will be justified, and by your words you will be condemned.”

38 Then some of the scribes and Pharisees said to him “Master, we want to see a sign from you.” 

39 But he answered and said to them “An evil and adulterous generation seeks after a sign, and there shall no sign be given to it, but the sign of the prophet Jonah.

40 For as Jonah was three days and three nights in the belly of a great fish, so shall the Son of man be three days and three nights in the heart of the earth.

41 The men of Nineveh shall rise in judgment with this generation and condemn it: because they repented at the preaching of Jonah; and, behold, one greater than Jonah is here.

42 The queen of the south shall rise up at the judgment with this generation, and shall condemn it: for she came from the uttermost parts of the earth to hear the wisdom of Solomon; and, behold, a greater than Solomon is here.

43 When the unclean spirit has gone out of a man, he walks through dry places, seeking rest, and finds none.

44 Then he said ‘I will return to my house that I came out of;’ and when he comes, he finds it empty, swept, and put in order.

45 Then he goes and brings seven other spirits more wicked than himself, and they enter in and dwell there: and the last state of that man is worse than the first. So it will also be with this evil generation.”

46 While he was talking to the people, his mother and his brothers stood outside, desiring to speak with him.

47 Someone said to him “Behold, your mother and brothers are standing outside, and wish to speak with you.”

48 But he answered the one who told him “Who is my mother? and who are my brothers?”

49 And he stretched out his hand toward his disciples and said “Here are my mother and my brothers!

50 For whoever shall do the will of my Father who is in heaven, the same is my brother, and sister, and mother.” 

For further reference: Matthew 12 in ESV, HCSB, NASB and NIV via Bible Gateway.