Three Models of Divine Sustaining
Theists believe that God is not only responsible for creating or bringing about (the initial state) of a world of concrete finite beings but also that God in some sense sustains those beings throughout their existence. But what does divine sustaining amount to? I'd like to identify three possible models of divine sustaining.
continuous creation: There is no fundamental difference between God's work in creating and sustaining. As long as creation endures, continuous activity on God's part efficaciously brings about the entire being of every existing created thing. This model is committed to an anti-conservation of created being principle: contingent beings cannot continue to exist, even for an instant, should God stop his sustaining activity.
infusion: There is a fundamental difference between God's work in creating and sustaining. Creating brings about the entire being of the creature. Sustaining does not. But sustaining is not mere conservation. It is a positive activity on God's part without which created things either (a) would gradually dissipate or (b) would not function optimally (even if they could persist indefinitely on their own), or (c) both. This model is committed to a limited conservation of created being principle: contingent beings can continue to exist for a time apart from divine sustaining, but they either cannot persist indefinitely or cannot function optimally apart from divine sustaining.
conservation: There is a fundamental difference between God's work in creating and sustaining. Creating brings about the entire being of the creature. Sustaining is merely God's refraining from annihilating a thing. This model posits a conservation of created being principle: things that exist automatically continue to exist unless something else destroys or annihilates them.
Now, I reject continuous creation because it seems to entail occasionalism (i.e., that the only genuine cause is God) and theological determinism. It renders creatures wholly passive with respect to God, in the same way that the image on the movie screen depends entirely at each moment on the light shining from the projector.
Either of the other two models are compatible with creaturely freedom, but one might worry that the conservation model is too passive on God's part. It seems to smack more of deism than theism.
The infusion model seems to me to strike the right sort of balance between continuous creation and mere conservation. It says that created things depend continuously on God not for the entirety of their being, but for either long-term existential stability and/or to be able to function at undiminished capacity. This allows creatures a limited independence of God, enough for creaturely freedom, without rendering divine sustaining a purely passive endeavor on God's part.