This phrase is used here to mark the beginning of a new part of the story. If your language has a way for doing this, you could consider using it here.
This could be translated as, "Why are you picking grain on the Sabbath?" It is a rhetorical question that means "Picking grain on the Sabbath is against God's law!" The word "you" is plural, and refers to the disciples. (See: [[rc://en/ta/man/translate/figs-rquestion]], [[rc://en/ta/man/translate/figs-you]])