Final answer:
Lady Capulet's line addresses the themes of the irrationality and futility of the ongoing feud and the foolishness of violence in 'Romeo and Juliet.'
Step-by-step explanation:
The line "A crutch, a crutch! Why call you for a sword?" from Shakespeare's Romeo and Juliet brings to light a significant theme of the play. Lady Capulet's words mock old Capulet's reaching for a sword, suggesting that he is too old to fight and should rather need a crutch. This moment highlights the theme of the irrationality and futility of the feud between the Montague and Capulet families, as well as the foolishness of violence and the idea that with age should come wisdom, not the perpetuation of long-standing conflicts.