One way in which this poem is important in Frankenstein is that it helps to set the tone and mood for the novel. It is set for the most part in the frozen northern seas, the kind of wild regions to which Walton, the intrepid explorer and frame narrator, is heading at the start of Frankenstein. Walton actually invokes the poem and its protagonist, the Ancient Mariner, in a letter to his sister and goes on to admit that
I have often attributed my attachment to, my passionate enthusiasm for, the dangerous mysteries of ocean to that production of the most imaginative of modern poets (letter II).
The poem, with its wild romantic setting and supernatural events, has inspired Walton to seek out the ends of the earth in a similar quest for adventure.
When narrating his own story, Victor Frankenstein also refers to ‘The Rime of the Ancient Mariner’, quoting a few ominous lines from the poem just after he sees the creature he made come to life for the first time, and which he has immediately come to regard as a ‘frightful fiend’ (Chapter 5) – a direct quote from the poem.
The poem, then, is invoked both by Walton and Frankenstein; and the figure of Frankenstein seems to exert a kind of fascination for Walton, just as the Ancient Mariner casts a spell on his listener, the Wedding Guest.
The poem is also very important in that it shares a major theme with the novel: the dangers of over-reaching, of trying to achieve too much. Frankenstein and Walton want to venture into places never before explored; Walton seeks to reach far-off places on the globe, while Frankenstein delves into the wildest realms of experimental science. Similarly the Ancient Mariner thinks he can challenge nature and shoots an albatross for no reason except that he can. But such audacity brings down great misfortune on his head as he loses all his crew and is forced to sail alone with the dead on terrifying seas. He has learnt his lesson by the end and seeks to pass it on to the awed Wedding Guest.
Frankenstein is also soundly punished for his presumption in creating the monster, and warns Walton against the dangers of unbridled ambition:
Unhappy man! Do you share my madness? Have you drank also of the intoxicating draught? Hear me, - let me reveal my tale, and you will dash the cup from your lips!’ (letter IV)