repression

• "He was austere with himself; drank gin when he was alone, to mortify a taste for vintages,"

  Utterson is a person with deep self control, he makes sure to repress his urges and limit his indulgence in things he enjoys.
• "I am ashamed of my long tongue,"

  Utterson is a curious person as well as a person who enjoys gossip but avoids it as it would break the unspoken Victorian gentleman code. As a result, he apologies to Einfield for talking about Jekyll and Hyde.
• "All that time my virtue slumbered; my evil, kept awake by ambition, was alert and swift to seize the occasion; and the thing that was projected was Edward Hyde,"

  Hyde is the definition of free will, he does as he pleases and that debatably makes him evil. As Jekyll remains separate from Hyde, his is a respectable citizen who stays virtuous. Meanwhile Hyde is the desires that stay hidden in the dark.
• "My devil had been long caged, he came roaring out,"

  The more that Jekyll repressed Hyde, the stronger he got and this resulted in him completely taking over Jekyll.
• "Hence it came about that I concealed my pleasures;"

  He was already living a life of duplicity long before his personality split into Jekyll and Hyde. Living in the Victorian era, Jekyll was compelled to satisfy his appetites in secret and further repress them to preserve his reputation as an upright citizen. It is never revealed what "pleasures" Jekyll indulged in, so the reader is left to surmise to what degree Jekyll's character was composed of evil before it split.
• "A great curiosity came on the trustee," "...and the packet slept in the inmost corner of his private safe."

  Utterson is tempted to ignore the instructions and tear open the letter, but stops himself. Utterson has become desperate to understand the mysteries behind Jekyll's behavior, and it seems Lanyon has something to say on the matter. But Dr. Lanyon is now dead, and Mr. Utterson feels obligated to honor Lanyon's wishes. Utterson's professionalism allows him to repress his curiosity and maintain respect for his dead friend's wishes.
• "...The more it looks like Queer street, the less I ask," ""A very good rule, too." said the lawyer"


  Mr. Enfield actually is an inquisitive man, but he represses that aspect of his character because he thinks it is dangerous.