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Line. 482-485: for neither do.....with zeal.
At Hell's conclave, Satan undertook the hazardous Journey to Earth to tempt man and seduce him from God. Every one of the assembled angels praised him for his daring and his spirit of sacrifice. At this point in the story Milton makes these general observations upon the conduct of the bad angels.
Just as bad men do not lose all their virtue, so neither do the spirits damned lose all theirs. They retain some of their good qualities, such as this disinterested praise of Satan's virtue, in order, as it were, to prevent bad men from boasting that they are superior to the devils, from their having done dees which appear admirable on the surface spurred by selfish ambition or a zeal for personal glory.
Milton explains from a worldly point of view why the devils retained some of their virtue yet, though they had been cast into Hell.