Luke 6:2 Meaning

1And it came to pass on the second sabbath after the first, that he went through the corn fields; and his disciples plucked the ears of corn, and did eat, rubbing them in their hands.

2And certain of the Pharisees said unto them, Why do ye that which is not lawful to do on the sabbath days?

3And Jesus answering them said, Have ye not read so much as this, what David did, when himself was an hungred, and they which were with him;

4How he went into the house of God, and did take and eat the shewbread, and gave also to them that were with him; which it is not lawful to eat but for the priests alone?