After the fallen Angels decide to corrupt the new world that God has created, Satan volunteers himself as a scout. Satan is the leader in command of the fallen angels and this is symbolic in that military heroism is displayed, showing how Milton favors the military organization of the fallen angles. Also, by Satan sacrificing himself as a scout before the others is, I believe, an underlying reference to Heaven, as Jesus sacrificed himself for all. As Satan approaches the gates of Hell, he sees nine gates: 3 of brass, 3 of iron, and 3 of adamantine. Guarding the gates are two figures: one is half woman and half serpent named Sin and the other is a dark figure named Death.  Both of these figures claim to be offspring of Satan from when he was outcast from Heaven. Again, there is a Heavenly reference to God’s son Jesus, as Sin and Death are to Satan. Satan explains his plot to corrupt the new world made by God, and the figures unlock the gates and Satan sets off on his journey through Hell to find the new world.