The predecessor to yoga was pure spiritual discipline. Every time I unroll my mat to practice I am participating in the practice of heat, preparing an alchemical brew to transform myself and the world. Every time the mat rolls out more heat builds by pure discipline. I’ve watched the heat change my muscles, tendons, and bones, and the difference in my mind is apparent.

The spiritual side is felt by practice, not easily written.

Nature is constantly at work toward this end. Its own calor inclusus or innate heat slowly transmutes the stubbornly resisting primary matter. The alchemist, however, by ingeniously intensifying the heat, could hasten nature’s own aims. In his laboratory and at his stove the adept believed he could bring to fruition in a lifetime, or sooner, what nature by itself takes centuries to accomplish.

† James Hillman - Alchemical Psychology