‘Now it came about on a sabbath, that he was going through the grainfields, and his disciples plucked the ears, and ate, rubbing them in their hands.'
On this particular Sabbath Jesus was walking through a grainfield with His disciples. The Law of Moses allowed anyone walking through a grainfield to partake of the grain for his own needs, but not to put in a sickle (Deuteronomy 23:25). This was to be of especial benefit to the poor. Thus the disciples were within their rights in what they were doing. They were plucking the grain, rubbing it between their hands in order to rid it of the husk, and then eating it. But as they were not used to being too strict about Sabbath Day observance they had failed to recognise that this might cause offence.
For the ‘Elders' had laid down the principle that reaping and threshing were not allowed on the Sabbath for they were to be seen as work. Jesus would not have disagreed with that. Where the controversy came in was in interpreting what the disciples had been doing as ‘reaping and threshing'. He would have been able to point out that reaping and threshing someone else's field would have been frowned on as breaking the Law (they must not put in the sickle), so that as the Law allowed what His disciples were doing it was not seen as reaping and threshing. But the Pharisees saw it otherwise, and the synagogue elders would probably have backed them.)Under later interpretation they would have been able to do what they did to amounts less than the size of a dried fig, so pedantic had things become). So Jesus will advance another argument which will also emphasise His own authority.