Expositor's Bible Commentary Commentary Mark 2:24

"And the Pharisees said unto him, Behold, why do they on the sabbath day that which is not lawful?" — Mark 2:24 (ASV)

The main point at issue here was not the act of harvesting the heads of grain in fields that did not belong to them. Such activity as Jesus and his disciples were involved in was explicitly allowed in the law . What the Pharisees objected to was doing this reaping and threshing on the Sabbath.