It is often insufficiently appreciated, I submit, that so-called “classical theism” is not a monolithic model of God. There are two main varieties:
- Unqualified classical theism (UCT) = God is absolutely simple, absolutely immutable, absolutely timeless, absolutely impassible, purely actual, etc.
- Qualified classical theism (QCT) = God is significantly simple, significantly immutable, significantly timeless, significantly impassible, etc., but not necessarily as absolutely as UCT would have it.
By “significantly” as opposed to “absolutely” I mean that there are important respects in which those adjectives apply to God, such that it is appropriate in many contexts to describe God as “simple” etc. without needing to add on precisifying qualifications. For example, it’s appropriate for me in ordinary contexts to describe my desk as “flat” without qualifications like “mostly” or “approximately,” even though I know full well that it’s not absolutely flat. If I viewed the surface of my desk with an electron microscope, it would appear anything but flat. For nearly all practical purposes, however, “flat” is a perfectly appropriate adjective. Similarly, according to QCT, God can (in normal contexts) appropriately be described as “simple” etc. without thereby committing one to the idea that God is absolutely simple etc.
It’s easy to conflate UCT and QCT because influential writers in each camp often use the same terminology without bothering to state how absolute they take these attributes to be. For example, the Cappadocian fathers agreed with Augustine that God is “simple,” but they didn’t mean the same thing. The former affirmed an essence/energies distinction which entails that God is not numerically identical to His essence, whereas the Augustinian tradition affirmed that identity (and thus rejected the essence/energies distinction). By describing God as “simple” some theologians may have meant merely that God is mereologically simple, i.e., not decomposable into separable parts like composite physical objects are.
Similar remarks apply to the understanding of impassibility, as Paul Gavrilyuk has argued. Not everyone who described God as “impassible” understood this in an absolute sense. As understood by UCT, impassibility means, roughly, that God cannot be affected in any way by anything extrinsic to Himself. As understood by QCT, however, impassibility may mean merely that God can’t experience negative emotions, that He cannot be overwhelmed or hindered by negative emotions, or that His intrinsic happiness cannot in any significant way be diminished by creaturely events.
Likewise, immutability, as understood by UCT, means that God cannot change in any respect whatsoever. For QCT, in contrast, it may mean merely that God is morally immutable or perhaps that He is immutable in essence without necessarily being immutable in accidents (i.e., accidental intrinsic properties).
Even a description like “timeless” (achronos in Greek) is potentially ambiguous. It can mean absolutely timeless, i.e., having no relations to time or change whatsoever. However, since Chronos (“Time”) was the Greek name for the planet Saturn, “achronos” applied to God could mean merely “not within the Saturnine sphere of the Ptolemaic cosmos.” In other words, descriptions of God as “timeless” in some authors could mean merely that God is not continually changing akin to the motions of the planets and other heavenly bodies that we use to mark the passage of time, but rather that God is fundamentally stable like the so-called “fixed stars.”
My main point is simply this: If you find an ancient or patristic author who applies terms like “simple,” “immutable,” “impassible,” and “timeless” to God, don’t assume they necessarily mean these terms in an absolute sense. That has to be judged based on careful assessment of the textual and historical context.