Jack the Ripper: I shall tell you where we are. We're in the darkest region of the human brain, a radiant abyss where men go to find themselves.
Netley: I don't understand, sir.
Jack the Ripper: Hell, Netley. We are in hell.
Sir William Gull: No man amongst you is fit to judge the mighty art that I have wrought. Your rituals are empty oaths you neither understand, nor live by. The Great Architect speaks to me. He is the balance where my deeds are weighed and judged, not you.
Sir William Gull: One day men will look back and say that I gave birth to the Twentieth century.
Answer: In the original book, Merrick's appearance is used to show William Gull's education, expertise as an anatomist and that he recognises and respects cultural diversity - Gull assures Merrick that, had he been born in India, he would be worshipped as a descendant of the elephant-headed god, Ganesa. In this spirit, Gull even offers the victim of his first Ripper slaying to Ganesa as a sacrifice, as Indians make a sacrifice to Ganesa at the beginning of an important enterprise. Merrick is present as a vehicle to establish the rich nature of Gull's character. When it comes to the film, however, this subtlety is completely lost - it seems very much that the scriptwriter noted Merrick's appearance in the book and felt that it would be cool to include the character in his script. As such, as you point out, it does feel that Merrick's presence, stripped of the subtleties of the book, is almost entirely pointless.
Tailkinker ★