Matthew 12:
 1 At that time Jesus went through the grain fields on the Sabbath. His disciples were hungry and began to pick some heads of grain and eat them.  2 When the Pharisees saw this, they said to him "Look! Your disciples are doing what is unlawful on the Sabbath."
 3 He answered, "Haven't you read what David did when he and his companions were hungry?  4 He entered the house of God, and he and his companions ate the consecrated bread—which was not lawful for them to do, but only for the priests.  5 Or haven't you read in the Law that on the Sabbath the priests in the temple desecrate the day and yet are innocent?  6 I tell you that one greater than the temple is here.  7 If you had known what these words mean, 'I desire mercy, not sacrifice,' you would not have condemned the innocent.  8 For the Son of Man is Lord of the Sabbath."

This is a theological discussion according to Jesus concerning the very nature of God and not just an infraction of a rule.  The Pharisees in true pendulumic fashion have made the Sabbath about measuring the performance of personal discipline.  They have been so focused on filling in with their technical noodling that the song has disappeared behind the scales they play.

Jesus cuts out the excess and returns to the heart of God’s Creation song.  On the seventh day God rested.  What is Sabbath for?  Why are we invited into God’s Sabbath rest?

In the childhood song of Bible history, Jesus sings the verse about David and his pals walking in to the Temple and eating the holy bread.  Technically it was for the priests, but a unique situation arose.  David and his companions arrived at the Temple very hungry.  They were on assignment from the King and were famished. 

The priest did not have anything but the Bread of Presence, an offering put daily before God.  In poetic styling, the bread offered to God is shared mercifully with those who were not entitled to it.  Mercy is very much like that.

And then Jesus sings the next verse about the priests working in the Temple on the Sabbath, and not guilty of Sabbath-breaking.  Mercy understands the heart of the matter and expresses the truest melody.

Mark 2:
27 Then he said to them, "The Sabbath was made for man, not man for the Sabbath. 
Simply brilliant…  God created a pregnant pause in our life in which we could rest and be renewed by His friendship.  God created the Sabbath for us.  It was not all about Him.  It is a precious gift to His people.  Why do we want to reschedule our appointments with God?