‘But he said to them, “Have you not read what David did, when he was hungry, and those who were with him, how he entered into the house of God, and they ate the showbread, which it was not lawful for him to eat, nor for those who were with him, but only for the priests?” '
Jesus replied from a well known passage concerning David (1 Samuel 21:1-9). There David and his companions had, ‘because they were hungry', persuaded the High Priest of the day to let him and his men have the old showbread which had been taken from the Table of Showbread in the Tabernacle when, as was the custom, it had been replaced. This was ‘holy' and could only be eaten by the priests. But David had pleaded special circumstances and that his men were in a state of consecration, and his plea had been allowed even though ‘it was not lawful'. No one, not even the Scribes, had ever criticised David for this, or even did so now, because he was seen as having been God's anointed. So one of Jesus' points will be that as the Greater than David as ‘the Son of Man', He has an even better right to determine Sabbath law. What David could lawfully do for himself and his men, He could lawfully do for Himself and His men. He could interpret the Law in their favour.
Another point that may have been in Jesus' mind was that David had claimed the right because he was on the king's business (even though in David's case it was a lie). This, connected with Jesus statement that as Son of Man He was Lord of the Sabbath, may signify that He considered that His disciples were ‘on the King's business', that is, serving the Kingly Rule of Heaven. Jesus seems very much to have seen He and His men as parallel with David and his men.
Note here that David ‘went into the house of God' (singular) while his men who ‘ate' (plural) did not. Thus he was demonstrating some kind of right to enter the house of God. This may be intended to lead on to Jesus claim to be greater than the Temple.