What is juxtaposition in chapter 9?

Aunt Harriet wanted to swap babies with her sister Emily to get a certificate since her baby is a Deviant and Emily’s baby (Petra) is perfect. However, Emily and Joseph accuse her of being used by the Devil to trick them to commit a conspiracy and heresy. She is found dead in the river later, possibly by suicide. This tragedy is juxtaposed with the birth of a super telepathic communication ability.