以上は is used when the speaker treats something as an established fact or decision and then draws a logical consequence. It often carries a sense of responsibility or determination: since you have done X, you must do Y. The clause before 以上は is the reason, and the clause after is the result or obligation. It is more emphatic than から or ので, and it is common in speeches, formal statements, or when someone is admonishing themselves or others. For example, if you say '約束した以上は守る', you mean that since you made a promise, you have no choice but to keep it. The pattern is typically used in written or formal spoken contexts, and it sounds strong, so it is not used in casual chit-chat.