THE LAST WORD By Paul Micou (Bantam, $255) THIRTY-FIVE years ago, Matthew Richmond's uncle Ian had a series of highly informal conversations with God. Uncle Ian transcribed his notes and published The First Word. Every five or six years he published an updated account of his private tete-a-tetes with the Creator and revealed them to the world. As the novel opens, the Last Word, the seventh in the series, is about to be promulgated. The Seven Seals of Revelation, it seems, are not only the province of the late David Koresh and his Branch Davidians in Waco, Texas. Uncle Ian's genius is that he has combined the American fetish for television evangelism with the even more fervent American fetish for being thin. Movie stars and professional athletes cleave to the Word and millions of other Americans - those who wouldbe saved and those who would love to lose a little weight - flock to Ian's cause. He maintains an Institute of the Word in an ornate but tasteless mansion atop a hill on the coast of New England. From there, he disseminates his word, encourages research into life, death, and the after-life and spies on his promiscuous wife by means ofan elaborate satellite system. The most remarkable gesture God makes to Ian is revealing to him, in the original conversation, the date of Ian's death. The whole history of Wordism is bound to The Date, and The Date falls three days after the novel opens. The narrator, Matthew Richmond, is Ian's nephew. Ian has chosen him to be the heir to the Word and its Institute. On The Date, Matthew and Ian sail off into the Atlantic. Ian apparently drugs his nephew and vanishes. Matthew sails back to Gawpassat, assumes control of the Institute and discovers that his flamboyant uncle has left him a hollow shell. The Last Word is the perfect yuppie novel: cynical, spiritually empty, devoted to wealth and self-serving. What rescues it is its delightful breezy style and a devotion to unyuppie-like irony. Yuppies, like evangelists, take themselves seriously, don't they? This novel refuses seriousness; its comedy is light-hearted even if its themes include a close-up portrait of greed and its willingness to prey on people's capacity for self-delusion in the name of God.