He entered again into a synagogue; and a man was there whose hand was withered. They were watching Him to see if He would heal him on the Sabbath, so that they might accuse Him. He said to the man with the withered hand, "Get up and come forward!" And He said to them, "Is it lawful to do good or to do harm on the Sabbath, to save a life or to kill?" But they kept silent. After looking around at them with anger, grieved at their hardness of heart, He said to the man, "Stretch out your hand." And he stretched it out, and his hand was restored. The Pharisees went out and immediately began conspiring with the Herodians against Him, as to how they might destroy Him.
As was his usual practice, Jesus is prepared to teach in a synagogue, and there is a man who needs to be healed. The Pharisees were ready to accuse him of breaking the Sabbath, because he was about to do his usual “work”—healing the sick, which allows him to be fed. They saw Jesus’ ministry as a “job” that he needed to cease on the Sabbath day. Jesus challenged them, showing that he saw his ministry as simply doing good to whoever as had need, and that the Sabbath day was a day to do good, even as any other day of the week is. Their silence in response to his question was a challenge right back to Jesus. Jesus was furious, then and called the man in front of everyone there, and healed him openly, in defiance of the Pharisee’s tradition.
The Pharisees were extremely upset and began making plans to destroy Jesus. Why? Because, first of all, he made it clear that he opposed their political agenda to have all of Israel live out a strict Sabbath. Secondly, Jesus showed himself to be in rebellion against their laws of the Sabbath—and breaking that law was punishable by death (Exodus 31:15). Thirdly, Jesus was popular, and getting more popular all the time, and so he might be a political rival against the Pharisees, at least in Galilee.
The Herodians were servants of the house of Herod, who was interested in retaining their political control over Jewish territory, especially Galilee. Jesus was already a threat to Herod, because his message of the kingdom was in opposition to all current rulers of God’s people—including the Herods.
Most people consider the Sabbath to be a matter of not working. To get some rest, to offer balance in life. Jesus, however isn't interested in a balanced life, and He sees the Sabbath differently. The Sabbath is to cease working for oneself, but it is not to stop working for others. In fact, Jesus says, the Sabbath is specifically a good time to work for others.
Therefore, rather than taking Sunday (or Saturday, as that is truly the Sabbath, the seventh day) as a day to go to church and to watch football, the followers of Jesus will see this as a day to volunteer to do good for those in need. The Sabbath isn't for resting, but for doing good.
Note on other thing, please. Jesus defines "doing good" or love here by opposing it to their opposites. To do harm to someone is the opposite of doing good. And to do good is the same as saving a life, the opposite of which is to kill. Thus, love cannot be included in doing harm or by killing. So when Jesus says to love our enemies, we cannot love and kill. We cannot love and harm. When we decide what to do with our enemies, we must remember that harming them is not Jesus' way. If we claim it is, then we only do harm to ourselves.