And when sir mordred felt that he had his death’s wound, he thrust himself with the might that he had up to the burr of king arthur’s spear, and right so he smote his father king arthur with his sword holden in both his hands, upon the side of the head, that the sword pierced the helmet and the casing of the brain. and therewith sir mordred dashed down stark dead to the earth.
what is the main idea of this passage from morte d’arthur by sir thomas malory?

Sir Mordred fatally wounds King Arthur.

In this passage, we see a combat between Sir Mordred and King Arthur. The two are fighting with their swords. They each hurt the other one. However, when Sir Mordred is struck by Arthur, he sends his sword with both hands on the side of the king's head. The sword pierced the helmet and the skull, fatally wounding King Arthur.

the penalty for defying creon's decree is death, as can be seen in the tragedy. if you do obey him however, all is forgiven