Marsilio Ficino’s Platonic Theology, Volume I

The rational soul is immobile in its substance, mobile in its operation, and in its power partly immobile and partly mobile.

1What shall we say the nature of this third essence is like? Is it wholly immobile, or rather mobile? Certainly it is not altogether immobile, because it is itself the source of qualities flowing into matter, which are devoid of all rest. Every cause acts according to its own nature; therefore some power and likeness of the cause must be preserved in its work. If that essence, which is the cause of qualities, were wholly immobile, then, because it would act through its altogether immobile nature, the quality descending from it would retain within itself some immobile nature. Yet the contrary occurs. Quality has three things within it: essence, power, and action. All three are involved in motion. Its essence is generated and corrupted, and generation and corruption are effected through motion. Its natural power is likewise intensified and diminished: heat, for example, burns more or less fiercely. Whatever heats more or less at different times is undoubtedly changed. Action undergoes the same. The action of fire is heating; it heats water not in an instant but over time. Temporal action is called motion by everyone. Quality is therefore subject to motion in every respect.