Here's why:
* Offend is a verb, meaning to cause someone to feel upset or insulted.
* Offense is the noun form of "offend" and refers to the act of offending or the feeling of being offended.
Examples:
* Verb: He offended her with his rude remarks.
* Noun: His remarks caused offense.
Let me know if you have any other words you'd like to turn into abstract nouns!