So why did Jesus do work on the Sabbath as pointed out by the Pharasees? Why would he pick wheat with the disciplines and eat the food that was only for the priest in Mark 2?
There are many instances where some of God's laws appear to contradict each other, such as what happens when someone wants to keep the command to circumcise their baby on the 8th day and it happens to fall on the Sabbath. It is not the case that they were forced to sin by breaking on of the two commands no matter what they did, but that one of the commands was never intended to prohibit the other from being obeyed, and in this case, the Sabbath was not intended to prohibit circumcision on the 8th day. Likewise, the Sabbath was not intended to excuse priests from doing their duties, and the bread being meant only for the priests was not intended to be used as an excuse to let people starve, so they were held innocent.
There is a significant difference between someone harvesting wheat to sell on the market as part of their occupation and the disciples plucking a few heads of wheat, rubbing them together, and putting them in their mouth. So I would question whether what the disciples were doing counted as work, and even if it did, it would not be the type of work that the Sabbath was intended to prohibit.
So they were wrong for pointing out that Jesus was doing work on the Sabbath? Isn't that what the Sabbath was, being a day of rest, no work nor anything from sunset to sunset, and those who disobeyed would be put to death? (Jeremiah 17:21-27). It wasn't that Sabbath was an excuse to avoid doing good, but doing anything would mean death.Man didn't make that punishment, God did. Pharisees were corrupt in motives, but it doesn't mean that what they were saying was wrong.
In Jeremiah 17:21-27 is it speaking against being bringing their burdens to Jerusalem in regard to selling them as part of their occupation, such as with Nehemiah 10:31. The Sabbath is meant to take time away from our work or what profits us in this world so that we have time to do God's work and to grow in our relationship with Him both individual and as part of a community of believers. The Pharisees had all sorts of laws that governed everything such as how much someone could lift or how far someone could walk on the Sabbath before it counted as work, and then they would put a fence around that to make it even more stricter to prevent someone from accidentally getting close to doing something that was work, but all of these laws perverted what was supposed to be a day of rest into a legalistic chore, and completely missed the point of the command.
Jesus didn't criticize the law itself. Jesus, a Jew, picked out of all the days, a Sabbath, to pick wheat and eat the bread thats for the priest ( which like come on, if I was to just go up and just take bread like that, someone would rightfully say "hey stop taking that bread! That's against the law"), but he criticizes that they, the ones who knew the scriptures and the words of the prophets so well, didn't see that He was the fulfillment of that law. Sabbath was there to remember how God rested on the 7th day, and not honoring that means death. Jesus did all that to show that we are no longer under subjection to a day, His commandments now cover the commandments of the prophets "Love God", and " Love they neighbor as thyself". Upholding the Sabbath now, such like how Protestants uphold Sunday for the day of pentecost, are all for remembrance. But its not law anymore. What is upheld is still the importance of assembly and the structure of the church. But we are not subject to days.
Pharisees weren't spiritually stupid, they were spiritually blind.
In Matthew 12:1-8, the disciples were picking heads of grain and neither Jesus nor his disciples ate the bread that was only meant for the priests, but rather Jesus used an example of David eating the bread that was meant only for the priests in order to explain to the Pharisees why what they were doing was not unlawful. Jesus was born under the Law, so if you think that he broke its requirement to not work on the Sabbath, then you should think that he sinned, and therefore could not be our Savior.
To fulfill the law means to cause God's will (as made known in the Law) to be obeyed as it should, and this is how Jesus fulfilled it. In Galatians 5:14, it says that loving our neighbor fulfills the entire Law, so everyone since Moses who has ever loved their neighbor has fulfilled the entire Law, which means that it does not refer to changing or doing away with the Law, but to obeying it as it should be. In Matthew 22:36-40, Jesus summarized the Law as being about how to love God and how to love our neighbor, so love fulls the Law because that is what the Law is essentially about how to do. In Galatians 6:2, it says that bearing one another's burdens fulfills the Law of Christ, which does not refer to doing away with it, but to obeying it as it should be. In Romans 15:18-19, it says that Paul fulfilled the Gospel, which does not refer to doing away with it, but to causing the Gentiles to come to full obedience to it in word and in deed as it should be. In Matthew 5:17-19, Jesus said he came to fulfill the Law, not to abolish it, and the proceeded to fulfill it six times throughout the rest of the chapter by teaching how to obey it as it was originally intended to be obeyed.