Elohim Essaim Elohim Essaim i implore you means God on High, God of Hosts, God on high, God of hosts, I implore you. It is basically asking god to capture people’s attention. The phrase was translated from Hebrew.
There’s also another interpretation in the Book of Black Magic and it’s in Italian- || Grand Griamoire. Let me break it down step by step-
“Eloim” can be translated to God or Powers and “Essaim” can be translated to Locusts or Swarm. From this we can infer that Kaori is basically trying to offer her soul to the gods or angels or devils in exchange for being able to captivate the audience. A small price for a big task
Elohim Essaim Elohim Essaim is a chant common in manga and anime(ex-it occurs in Gugure! Kokkuri-san episode 12 this season).