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FOR a while it seemed that the Galactic Empire was dead. All the mystery and excitement had gone, and the drooling Monarchs of a Million Worlds, the supple imperial concubines, the hard-faced conquerors that we read about in the magazines were just going through the motions. Science-fiction turned away from interstellar pageantry and began investigating psychological and sociological themes.

But rotten as most of them were, Galactic Empire stories were still better than this new wave. Psy-fi writers abandoned suspense and action for epiphany and explanation. Their characters descended slowly, slowly into themselves and then emerged, slimy with some new knowledge, in the last chapter. And in that last chapter they would explain. You see... this makes it all so clear! It wasn't important that the rocketship got to Alpha Centauri after all; what really matters is that we now understand the superego. Or the sex drive. Or our place on the evolutionary ladder. Or whatever.

Which may be part of the reason why so many people devoured Dune when it was published in 1968.

But while reading Dune, I realized that it was more than a brilliant revival of the Empire. Herbert had invented a complete universe, as mad and beautiful, inexplicable and frightening as this one. For a few magic moments there my own life seemed like a plausible fantasy, and Dune was real. Herbert's universe was a totality which stretched far beyond the ends of sight, an incredible system which could never be understood or explained. His characters survive by flashes of insight and prophecy, and when their intuition fails, they die.

DUNE MESSIAH, which continues the story of Paul Atreides begun in Dune, will mean nothing to those who have not read its predecessor.

The main character of the first book is the planet Arrakis, a mystifying desert waste which has never been fully mapped or understood by those who call themselves its rulers. The planet's true owners, the Fremen, are a tribe who exist in total secrecy on the face of the desert. Their terrible purpose-to change the planet's ecology totally and transform it into a fertile land-is the force which transforms Paul Atreides into Muad'dib, a semidivine military leader who eventually topples the Emperor and becomes master of the Galaxy. Melange-an addictive spice grown only on Arrakis-gives Muad'dib the power of prerecognition which allows him to seize the moment and turn it to his advantage.

But Paul's power of prophecy also makes him realize that events are beyond his control. The terrible purpose of the Frement has absorbed him and made him its instrument:

Even the faint gaps were closed now. Here was the unborn jihad, he knew. Here was the race consciousness that he had once known as his own terrible purpose... He had thought within him to oppose the jihad, but the jihad would be. His legions would rage out from Arrakis even without him. They needed only the legend he had already become.

Dune Messiah takes up the story after the end of the jihad-holy war-which has made Paul the emperor and the deity of the known universe. As his empire grew, his psychic powers have grown, until he is forced to rely on them totally. But total prescience is a trap-it removes him from his sources of strength and turns his allies into tools.

And the growth of the empire has blunted the terrible purpose. The Fremen have grown used to the luxuries of empire and have moved from the open desert to the towns and begun to forget the cautions which the desert taught them. They have begun to waste water, formerly the worst sin in desert society.

Aligned against the new ruler are all the forces which held power in the old regime: the ancient noble houses, the Spacing Guild, the mystics and social engineers of the Bene Gesserit, and the genetic manipulators of the Bene Tleilaxu.

The plotters set off a radiation bomb which blinds the prophet and isolates him from all guidance except that of his own prophetic sense. Relying on prescience alone, he walks an unerring path until the crisis, when his prophecies desert him and he must be rescued by his allies. But he has lost his function, for he can no longer trust his prophecies or guide his followers. His terrible purpose fulfilled, he steps free of history and walks to a lonely death in the desert, following the Fremen code that blind men must not burden the tribe.

ALTHOUGH it may sound hard to understand, it's easy to experience. "The universe," Paul says, "is not a riddle to be solved." Herbert is not leading his readers by the hand, and those who are looking for explanations will probably get annoyed. But if you let Dune Messiah move you where it will, it can take you a long way. I was skeptical when I sat down to read the book. After all, I thought, Dune has said it all. But 50 pages into the book, I was right back there living it all, and my life seemed like a plausible fantasy again.

If you dive in and try to get it all, you'll probably come up with nothing. But if you take it a little bit at a time, then you can come away with some moments that will stay with you a long time. Herbert's characters are fascinating, because they shimmer with the incomprehensibility of every human being, elevated to a higher level: St. Alia of the Knife, the Reverend Mother Gaius Helen Mohiam, Scytale the Face Dancer-each moves in the story with almost mythic import.

So the Galactic Empire lives again in Dune Messiah. But changed, changed utterly: Sci-fi's excursion into psychological explication (and Herbert wrote a psy-fi book, The Dragon in the Sea, a seriously flawed story of catatonic shock on the ocean floor) taught Herbert that nothing can be understood or explained. The new Empire shimmers with terrible beauty-haunting, unforgettable.

Everybody should read Dune. Everybody should read Dune Messiah. We owe Herbert a lot-he may be the only man writing, in sci-fi or out of it, who can think like a planet. And St. Gildas knows we need to think that way. Life right now is a plausible fantasy-and not a very pleasant one. Read Dune Messiah and touch something real.