Some think that when it comes to religious world views that anything goes and that such views are beyond reasoned discussion. This is not the case and one task of theology is to demonstrate what is a sound understanding of God, or existence in general, and what is not.
It is the aim of this post to demonstrate that what is eternal cannot be subject to change. This is in answer to LDS believers and others who conceive of God, or gods, as subject to change, time and even parts and yet being eternal. This conception will be shown to be unsound theologically and in error. It will be argued that it is impossible for such a concept to be actual and belief in such a concept, while one is free to believe it, is not belief of the truth.
Time cannot exist without change and at a basic understanding of time that does not measure but simply refers to before and after, change cannot exist without time. One cannot define change without having a state before the change, initial state, and a different state after the change. If there is not an initial state then we cannot have an after state, so there is no change. If change is infinite in duration in the past then there is no beginning and so no initial state. Without an initial state we cannot define any subsequent state and hence we cannot have change. So, the premise that change is infinite in duration in the past is self contradictory. Hence, what is of infinite duration in the past does not change and change must be finite because it must have a beginning.
Thus, change, and with it time, must have a beginning and what is infinite in duration in the past cannot be something subject to time and change. Further, we cannot have something of infinite duration in the past because that is defined in terms of time and hence change. We can only have something that exists before time began and that something cannot be defined or conceived in terms of time or change. Eternal is not the equivalent to infinite duration in time because it also speaks of existence beyond time and beginning.
Any concept of anything, including a god, that permits change must be a concept of something that has a beginning that is comes into existence out of non-existence because it cannot be eternally existing before time. This is the chief problem with a concept of existence that limits existence to the changing material universe because such an existence must have a beginning, evidence supports that this is the case, and such a universe must come from non-existence by itself. Yet, this is impossible because what does not exist cannot bring itself to existence without already existing to do so. Even to argue it was random presupposes the existence of randomness as an eternally existing something but randomness only has meaning with change and so only begins to exist with change and time. Thus, the only coherent understanding of existence must include the existence of something not subject to time or change that is able to create the existence of things that change without itself changing.
Theology comes into its own to set some boundaries as to what this something is and properly excludes as unsound ideas of that something that are in any way defined in terms of change or time, such as LDS or pagan Greek concepts of gods.
These arguments are better made by others but posted here to challenge thinking on some basics of theology that are largely assumed by the Fathers and much thelogical discussion.