Whenever religion and religious practices are used like a hammer to hit people over the head with, religion is in deep trouble. Certain religious types were watching Jesus closely with the proverbial religious hammer in their hand, waiting to wield its force. It seems the disciples were picking grain on the sabbath, a forbidden action according to the laws regarding sabbath observance. Down came the hammer of judgement.
But like all religious laws, the exceptions are conveniently forgotten by those wanting to strike another “transgressor” of the Law in order to discredit him. Jesus reminds them of this inconvenient truth, as King David ate the bread in the Temple solely to be eaten by the priests. Even David succumbed to the exception to observance of the Law... he was hungry!!!
Religion lived and observed with a hammer in the hand is dangerous, indeed. Religion, healthy religion, demands dropping hammers of judgement and remembering the purpose of religion: to bring together realities that seem to be in opposition but are not: heaven/earth; body/soul; humanity/divinity; death/life.
Religion celebrates the binding together of these realities, forming a harmony not a separation. Eating grain on the sabbath, curing in the sabbath will hardly hurt the purposes of religion: the gathering of realities that seem opposite, even opposed, into a union of purpose.