Quote 1
"Farewell happy fields
Where Joy for ever dwells: hail horrors, hail
Infernal world" (1.249-51).
As a punishment for his sin, Satan must exchange the "happy fields" of Heaven for the "horrors" of Hell. As a result of their sins, both Adam and Eve and Satan must say "farewell" to their respective paradises, as if some notion of exile from one's "home" were intimately bound up with the idea of sin. Note also the alliteration in this line ("h" and "f" sounds), a sonorous effect that contrasts with the bleakness of the picture.
Quote 2
"How such united force of gods, how such
As stood like these, could ever know repulse?" (1.629-30)
Satan is proud of his army, so proud that he's absolutely baffled that it was defeated. He thinks that a force as strong as his should never have known "repulse." His pride was so blinding that he didn't realize that God would easily "repulse" such a band, even though they "stood" like "gods."
Quote 3
"For who can yet believe, though after loss,
That all these puissant legions whose exile
Hath emptied Heav'n shall fail to re-ascend,
Self-raised, and repossess their native seat?" (1.631-4)
Satan thinks so highly of his army that he has no doubts about their ability to "repossess their native seat." The pride he takes in his rebellion is evident as well in the fact that he grossly exaggerates ("emptied Heav'n") the number of angels who joined his rebellion (we learn later that only a third of the angels fell with Satan).