"Upon my head they placed a fruitless crown and put a barren sceptre in my gripe.”
Macbeth begins to spiral into deeper moral corruption
kingship is worthless without an heir-triggering his paranoia about Banquo and leading him to consider further bloodshed.
“Fruitless crown”-oxymoron-reflects Macbeth's awareness that his rule is unnatural and is void of legitimacy
“Barren sceptre”-oxymoron-usually a symbol of kingly power- being described as barren (a term used for women who cannot have kids)- evokes infertility and feminises Macbeth's power hinting to his impotence, Macbeth jealousy of Banquo because he is scared the Fleance will overthrow him=this Shows how his ambition is increasing as he is never satisfied and is constantly in a state if insecurity which leads him to commit more blood shed