What was the purpose of the occultist and why choose these victims?

Question

I'm talking about the movie The Conjuring: The Devil Made Me Do It

Spoilers Ahead

In the latest edition of Conjuring franchise, we get to see that a boy murders someone and then constantly tries to commit suicide. Later, we find that it had happened before. A girl murdered another girl and then committed suicide.
Now, who's behind all this? A daughter of a priest, who is an occultist. She practises black magic and casts spells on people. She cast a curse on David Glatzel, which later transferred to Arne. This curse has a unique signature. A person is murdered and the murderer commits suicide. Ed and Lorraine found two cases and mentioned there must be a connection between two victims.

Unfortunately, the reason was never established. Or I may have missed it. How is the priest's daughter connected to David and Jessica? What was her motive to cast a curse on them? How are these victims connected?

Answer 1

The Occultist wanted to summon a Demon. To do that, she had to perform a dark ritual, that involves a triangle of possessed victims: The Child , The Lover and The Man of God. Each must commit a murder and then commit suicide. The Occultist managed to successfully orchestrate one by making Jessica kill her friend Katie and then kill herself. Then the possession went to the Gletzel kid and eventually Arne, who killed his landlord and almost managed to make him commit suicide. The last possession was Ed Warren, who tried to kill Lorraine (and probably himself afterwards to complete his part) but was unsuccessful.

There was no personal connection between the 3, but the 3 locations the witch’s totems were placed geographically made a triangle around the home of the Occultist.