Author's decision to tell the story mainly from Utterson's point of view influenced the whole narration and was especially important to create the atmosphere of suspense. Dr. Jekyll was so much involved into the plot and consisted of two completely separate personalities that we could not get any reasonable story from his point of view. It would not make any sense from his dual perspective as he did not realize what he was doing while being Mr. Hyde.
The idea to create such a double personality character may have originated from author's own experience "as a young man [he was] concealing his double life from his parents"1.
The main part of the story is told from the point of view of Mr. Utterson who is Dr. Jekyll's attorney. His narration is supplemented by some different people's points of view which makes the story even more interesting and mysterious as each of them knows only a small part of it and any of them can explain everything in full. Mr. Utterson was so much fascinated in Hyde, that he saw things which were not easily seen for other people. In some way I think he wanted to join Dr. Jekyll's life.
All that makes the ending of the story even more surprising and unexpected. Using points of view of four other people makes this effect even stronger. These additional narrators are Dr. Jekyll, Mr. Enfield, Dr. Lanyon, and the maid. It is to show that every story is seen differently from different points of view and probably there is no one truth at all.
In such a case we cannot learn more than the certain person in the story watching the main characters does. We also cannot predict future events as we do not know plans of the main characters of the story - Dr. Jekyll and Mr. Hyde. "We get the story this way because it draws out the suspense, and the mystery, and the shocking nature that was sort of requisite for shilling shockers back in the day."2
Although Mr. Utterson is Dr. Jekyll's attorney, and he is not able to know about the situation as much as Dr. Jekyll himself. Moreover, he seems to be quite involved in other matters, like law and religion, so he is not inquisitive enough to make us familiar with every single detail of the situation he notices. He is a nice guy and he really cares of his friend but he tries to do his best not to get too emotional about the situation although he speculates about Dr. Jekyll and tries to lift the veil of secrecy. He does not even try to judge his friend so he just tells what he has seen or experienced. His relationship with Dr. Jekyll is really good and he has no reason to suspect him guilty anyway of what has happened. He does not express his opinions or suspicion. He is a good attorney that is why "he should be independent from Jekyll and from any other entangling alliances which might prevent him from giving a completely candid and objective opinion"3
This all is not to let us realize while reading that Dr. Jekyll and Mr. Hyde are in real the same person as long as possible. In spite of all the hints we are given while reading the story, we are not able to realize till we hear it from Dr. Jekyll that the transformation was not only physical. Dr. Jekyll has changed also morally and mentally. "Jekyll, like many middle-class men in Victorian Britain, to regard vice as secret pleasure."4 He has gradually turned into completely different person. The person that cannot control himself at all. The person who is just bad. Until the worse side of Dr. Jekyll's personality was less developed, he looked much different. He was much taller that Mr. Hyde and they could not wear the same clothes. It was like that for quite a long time but finally changed. They became the same person with completely evil personality which meant the end of Dr. Jekyll's life. The future events are totally unpredictable to us and we feel fully surprised when we get to know that Dr. Jekyll and Mr. Hyde are one and the same person.
The author chose to tell the story from Utterson's point of view as he is the one who could describe the whole story from the very beginning to the very end. Although Dr. Jekyll and Mr. Hyde would be able to tell us more not only about the present, but also the past and the future, we would lose most of the suspense in the story and would not get it in all as he died at the end. This fact is showing us that it was better idea to to present it that way as it did not end just in the middle of an action because it is how it would be if Jekyll would be the narrator, we could also lose whole point of intensity because he should have tell that he is in two personalities.
In my opinion the idea to present the whole story from Utterson's point of view rather than use Jekyll's from the beginning was crucial for expressing author's thoughts on one of the most important features of late Victorian society: "Victorian standards of morality that themselves create hypocrisy and evil"5. A dual personality of the main character is a metaphor and a representation of that world. The end of the story emphasizes the tragic outcome of the situation. Such a world could not survive. It must have died like the main character. There was no way out. It may also help us to realize that "we all have an evil side to our nature but keep it under control"6. Choosing Utterson's point of view should be considered the best possible choice of the author.
Robert Louis Stevenson, 2005, Dr. Jekyll and Mr. Hyde, Pocket Books: New York