"Of man's first disobedience and the fruit of that forbidden tree whose mortal taste brought death into the wold and all our woe" He is talking about the downfall of man. He is looking for inspiration and turning to the Holy Spirit.
"Hurdled headlong flaming from the ethereal sky, with hideous ruin and combustion, down to bottomless perdition, there to dwell in adamantine chains and penal fire" Satan was rebelling against God. God threw him out of heaven and into the flames. This resulted in never ending pain of fire and chaos for Satan.
"Nine times the space that measures day and night to mortal men, he with horrid crew lay vanquished, rolling in the fiery gulf, confounded, though immortal" Satan rolled around in the fire for 9 days. Had total absence of God. Sorrow and sadness all around.