This passage begins with the words "at that time", or "at that time" without specifying clearly when. However, it was a Sabbath.
To understand well the reason why the Pharisees gave so much emphasis to keeping the Sabbath day, let us see its basis:
The word "Sabbath" stems from the Hebrew “Shabbat" meaning "rest from work".
The first time the term appears in the Bible is in Genesis 2:2 and 3: "on the seventh day God ended His work which He had done, and He rested on the seventh day from all His work which He had done. Then God blessed the seventh day and sanctified it, because in it He rested from all His work, which God had created and made.” Because he had rested on the seventh day after six days of work, God blessed and sanctified, separating it from the others. This is the origin of the week: six days of work followed by a day of rest, which is the almost universal practice day for the good of all physical, mental, and spiritual blessing to those who seek closer communion with God on that day.
It appears for the second time when the "manna" was introduced as food to the Hebrews during their sojourn in the wilderness of Sinai (Exodus 16:23): manna was not to be collected on the seventh day, so they had to make provision on the previous day. Moses explained that the LORD said that the seventh day is rest, the holy Sabbath (rest from work) of the LORD.
Later, the seventh day of the week was confirmed, and other special days were declared Sabbath, when the law was given on Mount Sinai (from Exodus 16:23, e.g. Leviticus 16:31). Therefore, they became part of the ceremonial of Jewish law.
The law established how the Sabbaths should be observed by the nation of Israel, with detailed rules (Exodus 35:2-3, Leviticus 23:3, 26:34).
It is the only one of the ten commandment in Exodus 20 that is only ceremonial and of no moral concern. It is also the only one that is not confirmed to be observed in the New Testament. On the contrary, Paul teaches "let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths" (Colossians 2:16). There is no other mention of it in the Epistles and here it is in the plural because it is equalled to the other special days, also called sabbaths, when work was banned according to the Law of Moses.
The Jewish sect of Pharisees prided itself on imposing the Mosaic Law in all its details, and it added its tradition, which required more obligations from people than those required by law. The Pharisees were notorious for their hypocrisy, ritualism, false piety and religious intolerance.
The disciples followed the Lord Jesus and felt hungry. This reminds us of the words of Christ to the scribe who wanted to accompany him: "foxes have holes and birds of the air have nests, but the Son of Man has nowhere to lay His head" (Matthew 8:20). It was a sacrifice to follow Him.
The law allowed you to “pluck the heads with your hand, but you shall not use a sickle on your neighbour’s standing grain” (Deuteronomy 23:25). That is what the disciples did to eat the raw grain. However, the Pharisees said that what they were doing was equivalent to reaping and peeling the grain, work that was prohibited on the Sabbath, and accused them of illegality.
The LORD chose not to discuss the interpretation they made of the law, but used two examples to show that there were more important principles to observe than the precepts of the law, thus opening up justified exceptions:
To meet an urgent need: When David and his companions were fleeing to save themselves from unfair persecution from King Saul, and were hungry, they went into the House of God (the Tabernacle) and helped themselves to consecrated showbread, food reserved for priests only (1Samuel 21:3-6). This was indeed illegal (charge they made to His disciples), but God allowed it in that emergency. The LORD Jesus was the true King of Israel, and if the nation had given him the place He owned, His disciples would not be forced to eat the cereal grains they plucked in the field.
When the work is done in the service of God: the priests worked at the temple on Sabbaths as a legal obligation, thus profaning the Sabbath by killing and sacrificing animals and doing many other services, but they were blameless because they were done in the temple. The disciples did not exercise priesthood in the temple, but served in the presence of “Who was greater than the temple”: He himself. We are told that this sentence would be better translated as "What is greater than the temple". It is actually a more appropriate comparison, and in this case, what is greater is the Kingdom of God, present in the person of its King. If the temple was not subject to the Sabbath, less still was He that was greater than the temple. The Pharisees, who did not believe that Christ was the Messiah, must have been outraged with such a statement.
Again, the Lord Jesus quoted Hosea 6:6 "I desire mercy, and not sacrifice" (chapter 9:13). The Pharisees never quite understood the compassionate heart of God. Like them, many today mistakenly give more attention to compliance with practices and customs, than the main commandment of the Lord Jesus: "love one another" (1John 3:23). His statement that "the Son of Man is Lord even of the Sabbath" puts the Messiah in the position of representative of humankind and defends His superiority in this position. To the Pharisees it was blasphemy and it increased their hatred because it placed Him above their regulations.
Then the Lord Jesus went to the synagogue of the Pharisees, and a man with a withered hand being present, they put Him to the test, asking if it was lawful to heal on the Sabbath. The focus of attention was undoubtedly the man, and the Pharisees were looking for a reason to accuse the Lord Jesus. It was a challenge, because to be consistent with what He stated earlier, He would have to heal that man, breaking the law of the Sabbath. With this they admitted that He had the power to heal that man, and that when a man so disabled was placed before him, He would be moved by compassion to heal him.
The LORD again made use of an example to substantiate His answer: which one of them would not rescue one of his sheep immediately out of a pit where it fell, on a Sabbath? They could not answer, knowing that they could not deny that they would extend their hand to take it out, if not out of compassion, at least because of the value it represented to them.
The LORD then added, "of how much more value then is a man than a sheep?" And He gave a logical answer, “Therefore it is lawful to do good on the Sabbath." Without waiting for any argument he told the man to stretch out his hand, he obeyed, and it was restored to be as good as the other. The Pharisees, defeated, left and began to plot against Him among themselves, and also with their loathed rivals, the Herodians, on how they could destroy Him (Mark 3:6; Luke 6:11).
Until this time, the Pharisees had been watching the extraordinary things that the LORD Jesus was doing, no doubt checking carefully whether He fulfilled the law, and listening to what He said, and the opinion the people had about Him. They could not find any fault in what He did and said, and could not challenge the miracles made openly in front of all who were present. However, they rejected the idea that He was the Messiah who everyone expected, and were jealous of the admiration that people had for Him.
Whenever they confronted the Lord Jesus they were the losers, He clearly knew them very well and did not respect them. All this fed the hatred they felt for him, and now they were willing even to commit murder, breaking the greatest commandment: "you shall love the LORD your God… and your neighbour as yourself". The obstacle was the admiration that people had for Him.
1 At that time Jesus went through the grainfields on the Sabbath. And His disciples were hungry, and began to pluck heads of grain and to eat.
2 And when the Pharisees saw it, they said to Him, "Look, Your disciples are doing what is not lawful to do on the Sabbath!"
3 But He said to them, "Have you not read what David did when he was hungry, he and those who were with him:
4 how he entered the house of God and ate the showbread which was not lawful for him to eat, nor for those who were with him, but only for the priests?
5 Or have you not read in the law that on the Sabbath the priests in the temple profane the Sabbath, and are blameless?
6 Yet I say to you that in this place there is One greater than the temple.
7 But if you had known what this means, 'I DESIRE MERCY AND NOT SACRIFICE,' you would not have condemned the guiltless.
8 For the Son of Man is Lord even of the Sabbath."
9 Now when He had departed from there, He went into their synagogue.
10 And behold, there was a man who had a withered hand. And they asked Him, saying, "Is it lawful to heal on the Sabbath?"—that they might accuse Him.
11 Then He said to them, "What man is there among you who has one sheep, and if it falls into a pit on the Sabbath, will not lay hold of it and lift it out?
12 Of how much more value then is a man than a sheep? Therefore it is lawful to do good on the Sabbath."
13 Then He said to the man, "Stretch out your hand." And he stretched it out, and it was restored as whole as the other.
Matthew chapter 12, verses 1 to 13