A “sermon” in the broadest sense is a discourse on morality. And by morality I mean the rules of engagement in life – in other words the manual for living rightly (as opposed to wrongly). The incentive for living rightly – the carrot for following the rules in the manual – will of course be some sort of reward – heaven. The disincentive for disregarding the manual – living wrongly – will take the form of sort of punishment – hell. Virtue and vice represent the choices we face in approaching the rules. Virtue (following the rules) leads to heaven; and vice (disregarding the rules) leads to hell.
That’s also Stoicism in a nutshell. Follow the rules or suffer the consequences. Easy!