Forgive me if this has been asked previously and I just haven't seen it, but how exactly do the various Buddhas, deities, Bodhisattvas, Wisdom Kings, etc. function in Buddhism? What is their metaphysical status? Since Buddhism is concerned with a nondual Absolute or ultimate reality, how do the deities and other related figures function? I've heard they function has aspects of the enlightened mind that can be actualized through meditating on them, mantra, or other practices or that for example Manjusri represents the Buddha's wisdom, Vajrapani the Buddha's power, Avalokitesvara the Buddha's compassion, etc. but what exactly does this mean and how does it work?
For example, what exactly is Bhaisajyaguru and how can he assist in healing? How also do the theories surrounding mantra fit in with this?
Aside from direct answers, if anyone has any recommended books on these topics I'd be glad to hear them as well.