Augustine of Hippo

The sabbath was given to the Jews to be observed literally, like other things, as rites symbolically signifying something deeper. A particular kind of vacation, you see, was enjoined on them. Take care to carry out what that vacation signifies. A spiritual vacation, I mean, is tranquility of heart; but tranquility of heart issues from the serenity of a good conscience. So the person who really observes the sabbath is the one who doesn't sin. This, after all, is the way the command was given to those who were commanded to observe the sabbath: "You shall perform no servile work." "Everyone who commits sin is the slave of sin."