These "pre-existing spiritual beliefs" were, as Reider explains:

An aggressive conversion (brainwashing) is designed to break down pre-existing beliefs and replace them with new values and commitments.

The Tuareg are Islamic, but mixed with a "heavy dose" of their pre-existing beliefs including matrilineality.

Israelite monotheism evolved gradually out of pre-existing beliefs and practices of the ancient world.

The statistics on undecided voters indicate that most people have pre-existing beliefs when it comes to politics.

Selective perception is also an issue for advertisers, as consumers may engage with some ads and not others based on their pre-existing beliefs about the brand.

He in fact suggests that new technologies have had remarkably little effect on pre-existing human beliefs.

It seems to be an example of arriving at a conclusion that fits some "pre-existing belief"

They may seek to reaffirm a pre-existing belief, or act out of whimsy.

Narrative theory clashed with several pre-existing beliefs as to the nature of human beings and how they communicate and act.