The phrase "wast mercy of" is incorrectly spelled, as it should be "was mercy upon." The incorrect spelling likely stems from a misinterpretation of the archaic use of "upon" as "of." The correct pronunciation of "was mercy upon" is /wʌz ˈmɜːrsi əˈpɒn/ with the stressed syllables on "was," "mercy," and "upon." It is important to use proper spelling and pronunciation to avoid confusion and clearly convey meaning in written and spoken communication.