An intent or purpose; a why.
"The scientist pondered wherefore the chemical reaction had stalled, searching for the underlying cause of the failure."
Why, for what reason, because of what.
"She refused to answer wherefore he had left so abruptly."
Because of which.
"He left early wherefore he missed his own party."
The word "wherefore" comes from Middle English, combining the words "where" (meaning "what") and "for." It originally meant "for what reason," a sense that has largely been replaced in modern usage by "why.