Death threats were adopted from the Masonic orders and used to keep the practice of "spiritual wifery" a secret. And using secret handshakes helped insure that only insiders could access the dark corners of illegal behaviour.
As always, and even today the oaths of keeping a secret are designed more to keep people in a state of mind where protection of the church is paramount.
This allows the church to carry out its works with the protection of all participants willing to lie and decieve in order to keep its actions a secret.
And of course, freewill and agency means that members are perfectly free to follow without question.