(Mark 3:1-6 ESV)
But he was often found "working" on the Sabbath. This angered the Jewish leaders. They didn't like him working on the Sabbath and regardless of what he did, they saw his working to be more grievous... even if his work was one of mercy.
In this particular instance there was a man with a withered hand, a hand that was damaged that Jesus could do something about. Jesus could do something about it and the Jewish leaders watched to see if he would, even though it was the Sabbath and no work was to be done.
Jesus was not happy with their attitude, and called them on it saying, “Is it lawful on the Sabbath to do good or to do harm, to save life or to kill?” But they simply refused to answer him.
Jesus healed the man regardless, telling him to stretch out his hand. The man did so and was healed.
The Pharisees immediately started to plot against him.
I find that so sad. The rules were more important than anything else. I would find it hard living under that kind of hard and set rule.
But then I think of something. I used to work in social services. I was brought up under don't work on Sunday except for what is needful, and was raised to take work that didn't require me to work on Sundays. It took me mentally quite a while to reconcile working with special needs folk on Sundays as a needful job. It was something that needed to be done and working on Sundays didn't mean I was a bad Christian.
So sometimes it's hard to sort it out, but the Pharisees didn't need to be so hard-hearted and worrying about Jesus obeying the rules, instead of extending mercy to a man who needed it.
Doing needful work, showing mercy, and being a good servant of Christ is what we are called to do. Not worrying about keeping all the rules and remembering that God made the sabbath for us, not us for the sabbath.
This doesn't mean that we should be disrespectful of the day of rest that God gave us. He gave it to us for our own good health.
So just working on Sundays "just because" isn't something we should seek out. Neither should we feel guilty though if we are doing work that is needful.