Frankenstein was written as a horror in the Gothic style, and uses themes of entwined love and fear throughout.
The young Victor has a fear of not knowing which drives him to his love of study, and ultimately to create his monster. This act of creation has been interpreted as symbolic of a fear of pregnancy, or of the usurption of the right of procreation. Shelley herself associated maternity with fear and death, due to her mother dying in childbirth, and her own loss of her first child. On seeing his creation, Victor does not feel maternal love, but fear.
The monster in many ways, is the physical symbol of societal fear. He is the embodiment of Victor's lack of respect for natural creation. Yet although the monster exemplifies fear, the incident with the blind man in Ch.12 shows how the monster is not fear, but is feared due to external reasons. He creates fear by others' perceptions of him as monstrous. Fear is externally placed upon him and makes him into a monster. As the monster comes to perceive himself as an outsider and as one unloved by his 'parent', the fear and lack of love he receives from others drives him to seek vengeance on his creator - the one who should have loved unconditionally. The fear that others place upon him is the fulcrum for the monster becoming monstrous.
Although he tries please Victor, and then to create his own family for love, the monster remains a symbolic absence of (parental) love. Since the monster cannot have love, fear is all that is left: "If I cannot inspire love, I will cause fear!" (Ch.17). The monster tries to interpret his lack as power, saying "I am fearless, and therefore powerful." (Ch.20), yet he remains intrinsically linked to his 'father'. Once Victor dies, the monster also seeks death.
Frankenstein / Mary Shelley
The value of fright / Arthur Patterson [http://www.watershedonline.ca/literature/frankenstein/Frintro.html]
Frankenstein as Prometheus / Christopher Smith
On Shelley's Use of Nature Imagery / Bill Williams
The monster within: Mary Shelley's Frankenstein and a patient's fears of childbirth and mothering / B.R. Almond (IntJPsychoanal. 1998 Aug;79 ( Pt 4):775-86.)
The Enlightenment [Year 1 course] / University of Essex (1996/97) [Mary Woolstencraft & Mary Shelley]
Edited and updated essay:
To be added later