On the Mysteries (De Mysteriis)

they perceive. Likewise, [he thinks] that supplications are by no means suitable for the purity of divine minds. Iamblichus thinks they are suitable because of the inward sense that is inherent in supplications, especially those that are given by the divine. Pure intellects know sensible things without the use of sense.

Again on Supplications.

Porphyry says that certain material things are employed in supplications, and for that reason they are employed only for those gods who are animate beings. Iamblichus responds that in these material things, beyond corporeal qualities, there also lie hidden incorporeal and divine principles, forms, and measures, through which the things employed are congruent with the gods. Indeed, whenever anything is applied that is in any way agreeable to and like the gods, the gods are immediately present, they are joined to it, they bestow gifts, and they hear prayers. A certain small congruence of our affairs with the gods is sufficient for us to draw something from them. For they are always most ready for this on account of their natural goodness and wonderful power. Indeed, a most powerful cause acts upon matter, even if it is meagerly prepared. Porphyry distinguishes daemons from gods by this: that the former are incorporeal, while the latter are corporeal. Iamblichus says that their substances and properties cannot be discerned by these means.