What is a sermon? Is it different from a lecture or a talk? Can this word also be used in a negative way or as a joke (as in “my mother’s sermon about getting my work done on time…”)?
A sermon may be defined as a discourse for the purpose of religious instruction while lecture is discourse for the purose of instruction on any general topic and talk can be a formal as well as an informal discourse delivered to an audience. No, it can't be used in a negative way or joke.