The Pharisees were annoyed that the disciples were doing servile work on the Sabbath, even though the act itself was allowed by Deut. 23:25. Spiritually it is said that the disciples were rubbing the ears, purifying them from the outer husks to reach the grain, by meditating on the Scriptures until they found "the inner marrow of love".[1][2]
Chrysostom: " Here admire the disciples, who are so limited in their desires, that they have no care of the things of the body, but despise the support of the flesh; they are assailed by hunger, and yet they go not away from Christ; for had not they been hard pressed by hunger, they would not have done thus. What the Pharisees said to this is added, The Pharisees seeing it said unto Him, Behold, thy disciples do what is not lawful to do on the sabbath."[3]
Augustine: " The Jews rather charged the Lord’s disciples with the breach of the sabbath than with theft; because it was commanded the people of Israel in the Law (Deut. 23:25.), that they should not lay hold of any as a thief in their fields, unless he sought to carry ought away with him; but if any touched only what he needed to eat, him they suffered to depart with impunity free."[3]
^John MacEvilly, An Exposition of the Gospel of St. John consisting of an analysis of each chapter and of a Commentary critical, exegetical, doctrinal and moral, Dublin Gill & Son 1879.
^Cornelius Cornelii a Lapide; Thomas Wimberly Mossman The great commentary of Cornelius à Lapide, London: J. Hodges, 1889-1896.