James Blish SF Gateway Omnibus. Black Easter, The Day After Judgement, The Seedling Stars

Best known for his Hugo Award-winning classic A Case of Conscience, Blish was one of the first serious SF writers to involve themselves with tie-in novels, writing eleven Star Trek adaptations as well as the first original adult Star Trek novel, Spock Must Die. This omnibus contains three of his long out-of-print works: Black Easter, The Day After Judgement and The Seedling Stars. BLACK EASTER: A gripping story about primal evil: a sinister intermingling of power, politics, modern theology, the dark forces of necromancy, and what proves, all too terribly, not to be superstition.
THE DAY AFTER JUDGEMENT: Develops and extends the characters from BLACK EASTER. It suggests that God may not be dead, or that demons may not be inherently self-destructive, as something appears to be restraining the actions of the demons upon Earth. THE SEEDLING STARS: You didn't make an Adapted Man with just a wave of the wand. It involved an elaborate constellation of techniques, known collectively as pantropy, that changed the human pattern in a man's shape and chemistry before he was born.
And the pantropists didn't stop there. Education, thoughts, ancestors and the world itself were changed, because the Adapted Men were produced to live and thrive in the alien environments found only in space. They were crucial to a daring plan to colonize the universe.