In lines 120 - 160 of the first book of Paradise Lost by John Milton, we see several themes. A major one is that of despair versus hope. (Some Christians believed that despair was an unforgivable ‘sin’ against the Holy Spirit because it presumed God/prayer to be powerless to change things.) When Satan looks around after his ‘fall’ he sees myriads of fallen angels lying like faded scraps on the surface of a fiery hellish lake. In this setting and context (a dizzying fall from grace to a painful hell hole of defeat) they are demoralised and despairing. Though astonished, shocked and emotionally distressed by his own experience, Satan still appears to have a shred of hope left, so obviously his punishment hasn’t worked. Or it could be that God (as Satan says himself) has deliberately left them all with some sense of strength and will - all the more to fully experience the pain and sorrow of their new humiliating situation.
Satan tries to inspire the fallen angels to regroup and to try again and not just ‘rue the dire event’ that lost them Heaven. He believes that their defeat is not absolute and that ‘vigour soon returns’ even though he seems aware of God’s ulterior motive in allowing them all a little strength. God did this so they would have just enough energy to appreciate and suffer from their new painful situation, but Satan believes they can use this little bit of energy to good effect in regrouping their ‘army’ of fallen angels against God. Although doubtful of God’s omnipotence before, Satan now admits he was wrong about God whom ‘I now of force believe Almighty’ as he thinks God must be all-powerful in order to defeat Satan’s own ‘Invincible’ forces.
In the last lines of the passage he explains to his fallen angels that yielding to their fate of suffering is pointless as they may as well try to regroup and redouble their efforts to be a force for evil. He suggests that they oppose or destroy all the good that God tries to do in the world ‘to do ought good never will be our task, but ever to do ill our sole delight.’ He, of course, will lead them into battle again in the fight of evil against good.