Literary techniques (or more commonly referred to as devices) are chosen by writers specifically to provide mood, tone, or movement in their texts.
In Mary Shelley's Romantic novel Frankenstein, she uses imagery to depict the horror of Victor and the scene where the his monster first comes to life. Imagery is what an author uses to allow the reader to form mental images of the scene depicted.
In chapter five, Victor states that the night is a dreary one.
It was already one in the morning; the rain pattered dismally against the panes, and my candle was nearly burnt out, when, by the glimmer of the half-extinguished light, I saw the dull yellow eye of the creature open; it breathed hard, and a convulsive motion agitated its limbs.
Here, readers can visualize a night, tormented by the weather, and defined by the attempt at life by Victor's monster. The opening of the eye can send shutters through the engaged reader--they will (hopefully) feel the same fear felt by Victor as the monster again opens his eye.
The imagery of the cold and rainy night, the depiction of "yellow skin scarcely covered the work of muscles and arteries beneath," and the intense fear of Victor all pull together to form an image as horrifying as the idea of piecing together a man. Therefore, the meaning conveyed through the imagery depicted in chapter five is meant to horrify the reader.