The mind of the self-righteous person becomes obsessed with the little things that he chooses to pin his righteousness to. Everything else is viewed out of proportion, and the weightier matters of the law like judgment, mercy and faith become nothing, while the little things like the proud external conformity to some specific rule become everything. The Sabbath was given by God and while it was in force it was important for every Jew to keep it, but from the start it had its proper place and its proper usage.