Christless religion always cancels any real relationship with God, reducing it to a set of rules.  Of course, before Christ, apart from a few people who God filled with His Spirit, it was not possible to know Him personally. The Old Testament Law was clear about what God loved and hated, and how sacrifices could atone for unintentional sins (Numbers 15:27).  But there was no dynamic relationship with Father God.  Without that personal fellowship, religious people compile rules for life; wrongly assuming that by keeping them, God's wrath will be appeased.  The more intense that belief, the more rigorous the rules.  It happened in Jesus' day with Pharisees adding many regulations to God's law (Luke 11:37-52) ... and it still happens today.

Jesus brought a breath of fresh air.  He said that God designed the Sabbath.  It was a law which protected and provided for people.  Nobody is designed to be a perpetual motion machine!  We are also designed to worship God (and not our work or ourselves).  So, the Sabbath was one day away from work in order to be refreshed in body and in spirit - hearing God's Word and worshipping Him.  

Alas, that relational purpose was obscured by many legal definitions (invented by religious lawyers) of what 'work' meant.  One said that rubbing grain in the hands, to remove the husk and have a snack while on a country walk, was breaking the Sabbath law!  Jesus pointed to 1 Samuel 21:1-6 where David's men were very hungry.  Although the only bread available was specially consecrated and reserved for the priests, it was given to the group of bodyguards.  God knew that the bread was necessary to sustain them.

Of course, it was God who first defined the Sabbath (Genesis 2:2-3).  So, Jesus asserted His Deity by saying that He had the right to define what is acceptable to God on His special day.  Because He is the Creator, He knows what is 'fit for purpose'.  He knows when we are personally fulfilling the purpose He intends for us (Psalm 119:33-40).  He knows when we are in real relationship with Him and working with Him for the sake of His glory.  Every day at work or at home is a divine assignment to work with God; so, we must be careful that we do not constrict His plan for our daily lives by little rules which He has not given.  At the same time, we must not be so arrogant as to ignore what the Bible clearly commands. God wants us to be 'fit for purpose'.  His Word and His Spirit will guide us securely and show us how to interact with our Maker.