Jews, because they are still waiting for the Messiah to come, continue to observe the Sabbath law. No work on the Sabbath.
Christians aren’t under the Covenant God made with the Jews. Jesus is our rest. He is the fulfillment of the Law. We celebrate the Lord’s Day which is Sunday, the first day of the week. (And Catholics can go to Mass on Saturdays as well.)
If the work is necessary, then the Christian works. How would you feel if your child needed emergency medical attention but didn’t receive it because the drs, paramedics, hospitals, etc were all closed because no one was willing to give up their Sunday so that people could receive that help?
You say you want to be a priest. Well, like the priesthood, the medical profession is 24/7/365. So is the fire department.
Helping and taking care of others is a way of serving God. And that kind of work, whether one is paid for it or not, is not to be ignored Sabbath or no.