I've only read a summary and I'm going by memory. If I remember correctly, Victor Frankenstein feverishly worked hard to create the monster, intending it to be beautiful. After successfully bringing it to life, however, he realized how repulsive it looked and abandoned it. The monster became increasingly resentful, eventually becoming homicidal because of the people's reactions to it. It was only then Victor had to destroy the monster.
Now that I think of it, it has themes of parental abandonment due to disappointment with a child, whom grows up as a criminal afterwards. Self-hatred over physical appearance is another. The monster reads
Genesis 1-2 and concludes its creator must've been the devil himself, being nothing like Adam. There's also a desire for a companion which only Victor could provide, but intentionally botches it halfway out of fear of them reproducing. This finally broke the monster, leading to the killing spree. Finally, there's remorse over a burned bridge that's now too late to rebuild, and the monster decides to commit suicide by self-immolation. Victor was the monster's only family.
Essentially, it's a tragic story about an ugly child that was abandoned, never felt loved by man nor God, grew up to be a murderer, and then commits suicide after realizing its poor life choices wasn't bringing it any peace in life.
Again, I'm only going by memory. It's been a long time since I read the summary.