I think that the phrase “devoted to God” is the key.
For instance, going along with curing the sick, serving in a soup kitchen on Sunday, providing the food and drink for fellowship after Mass, or even shoveling the walk up to church before Mass so that the people can make it it is certainly not against God’s law.
But that's what Christ was trying to tell us: doing things in the name of God and not in the name of one's hobbies or personal pleasure is not the same. Yet, the Bible is very clear that sabbath is a day of complete rest, even for the live stock.
Shovelling the walk up to church can be done on a Saturday. Again, such planning is in devotion to God, so as not to have to do it on a Sunday. Soup kitchen stuff can be cooked the night before too.