Q: how does a spiritual practice actually result in change? What are the psychological mechanisms? How can one change from a ‘this’ to a ‘that’?

A: It is not a process of ‘change’, but of evolutionary emergence. The larva does not change into a butterfly but instead becomes the fulfillment of its potential as a product of the evolution of Creation. To repeat, Creation is evolution by virtue of the emergence of potentiality into actuality. Intention of the spiritual will is sufficient. The seemingly ‘new’ represents the unmanifest’s becoming Manifest, just as unclenching the fist reveals the open hand.

Transcending the Levels of Consciousness: The Stairway to Enlightenment by David R. Hawkins