Special Deliverance

Novel, first published: Del Rey/Ballantine 1982

College professor Edward Lansing receives explicit instructions from a slot machine that translates him to an alternate world. He stumbles into an inn where he sees four men with skull-like faces playing cards and meets a company of puzzled pilgrims like himself: a jingoistic brigadier, a fanatic fundamentalist parson, a robot named Jurgens transplanted right out of City, a certified poetess, and a female engineer. All are from different worlds and different cultures and have no idea why they have been trapped on this world.
The company sets out for an unknown destination, and after a number of trials, each member of the quest disappears one by one, except for engineer Mary and Lansing. Some of the assorted dangers are familiar from other Simak novels; the company stops at a deserted cIty where the Brigadier and the Parson disappear through "portals" to other worlds, a device used in Destiny Doll. Lansing and Mary reenter a huge blue cube (its force-field had formerly rejected them) and find the four card-players.
The card-players are aliens from the far side of the galaxy "social workers" conducting a search for qualified humans. The human race is threatened with extinction, obviously by its own stupidity (an old Simakian lament), and is at one of the "crisis points" of its evolutionary process.
Humans from various alternate worlds have been recruited to this world to be subjected to a "test quest." (Earlier, Lansing and his sociologist colleague discuss the possibility that historic crisis points could be responsible for the existence of these alternate worlds.) Lansing and Mary have passed the test with flying colors and will be translated to a university where they will study how to become more fully human and join thousands of other humans in forming a new society.

Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.123-124