Heavenly Muse: The source of Milton's inspiration, identified with the Spirit of God that spoke to Moses.
Oreb, Sinai: Mount Horeb and Sinai, where Moses heard the voice of God.
Shepherd: Moses; referring to the chosen seed, the Jews.
Sion Hill, Siloa's Brook: Places in Jerusalem, the holy city of the Jews.
Aonian Mount: Mount Helicon in Greece, sacred to the Muses.
Argument: Subject (or theme).
Providence: God's plan for the universe.
Justify: To show the justice of. Milton states his purpose in this line.
Grandparents: Adam and Eve.
Transgress: To sin against.
For one restraint: On account of the command not to eat of the Tree of Knowledge.
Th' Infernal Serpent: Satan, who in the Bible takes the form of a serpent and tempts Eve to eat the fruit of the Tree of Knowledge.
What time: When.
Host: Army.
His doom wrath: Fate had more punishment in store for him.
Obdurate: Stubborn.
Ken: Can see.
Still urges: Always presses; afflicts.
Sulphur: Burning sulfur, called Brimstone, is often associated with God's wrath.
As far removed utmost pole: This image is probably drawn from Virgil's Aeneid, which situates Tartarus (Hell) twice as far below the Earth's surface as the heavens are above it.
Weltering: Writhing; thrashing about.
Study: Pursuit.
With suppliant knee: Pleading in a kneeling position.
Doubted: Feared for.
Ignominy: Disgrace.
Empyreal: Heavenly.
Apostate: Renegade.
Vaunting: Boasting.
Compeer: Companion of equal rank.
Of force: Necessarily.
Suffice: Satisfy fully.
Thralls: Slaves.
Cherub: Angel.
Aught: At all.
Laid: Calmed.
Impetuous: Violently forceful.
Slip the occasion: Miss the chance.
Satiate: Satisfied.
Afflicted powers: Stricken troops.
Reinforcement: Increase of strength.
Rood: A unit of measure between six and eight yards.
Leviathan: A huge sea beast mentioned in the Bible, here identified with the whale by Milton.
Night-founder: Overtaken by the darkness of night.
Invest: Covers.
Incumbent on: Resting upon.
Lights: Rests after flight.
The force Etna: An underground wind moves a hill torn from Cape Pelorus on the coast of Sicily, or Mount Etna, a nearby volcano.
Sublimed: Vaporized.
Involved with: Wrapped in mist.
The Stygian Flood: The River Styx in Greek mythology, one of the rivers of the underworld.
Sufferance of supernal power: Permission of heavenly power.
