Victor created the monster for a couple of reasons. First, he was always curious about this type of science (it was forbidden to teach it in the schools), and secondly, his fiance died and he made it his purpose to end death and to somehow be able to bring her back from the dead. Victor, as the creator had the responsibility to care for the monster (he did not), and to keep it from harm and harming others (he didn't), as well as helping it to understand itself and educating it (he doesn't do this either). Victor abandons the creature because he is horrified at what he has done.