The Celestial Venerable Used Me as a Pawn

Zhang Baixuan transmigrated to a strange world with a System called the Devouring System.

But the System seemed dead and couldn’t be used at all. For three years, Zhang Baixuan tried everything he could think of, but nothing worked.

Who could have expected that the System would suddenly awaken while he and his wife were training in a secret realm? It even said something completely baffling:

[System owner detected. Kill them to activate the Devouring System.]

What does that mean?