This refers to the trade of 'yes, yes' words, which occurs upon the soul's own anvil.

This couplet suggests that our words, even the simple 'yes-yes' responses we use daily, are not just casual utterances. They are deeply formed, much like metal hammered on an anvil. The "anvil of the soul" means every word originates from our innermost being, our true self. So, when we engage in the "business of words," be it in casual conversation or important discussions, remember that each 'ji-ji' carries a piece of our soul. It's a reminder to speak with intention and awareness, recognizing the profound origin of even our most common expressions.