A new book of stories from Bernard MacLaverty is a cause for celebration, but ''Matters of Life and Death'' is more than that, as it is - without question - the finest collection yet from a contemporary master of the form. Beginning with the sudden, nauseating terror of a family caught up in an explosion of shocking sectarian violence and ending with the white-out of an Iowa blizzard and a different kind of fear, ''Matters of Life and Death'' is a book about bonds and connections, made and broken, secret and known. Vivid, beautifully controlled and written with effortless skill and empathy, these stories are object lessons in the art of short fiction.