The other day, I was discussing God’s eternity with my good friend, Chris. The most difficult aspect of the concept is determining how to speak coherently of God’s eternity while also confessing our faith in the Incarnation. Below are two paragraphs from Boethius that help us define God’s eternity in the first place. I read Boethius in undergrad, but I hadn’t thought about these passages until I was reminded of them by Eleonore Stump in her book on the thought of Thomas Aquinas:
(Consolation of Philosophy) That God is eternal, then, is the common judgment of all who live by reason. Let us therefore consider what eternity is, for this makes plain to us both the divine nature and knowledge. Eternity, then, is the complete possession all at once (totum simul) of illimitable life. This becomes clearer by comparison with temporal things. For whatever lives in time proceeds as something present from the past into the future, and there is nothing placed in time that can embrace the whole extent of its life equally. Indeed, on the contrary, it does not yet grasp tomorrow but yesterday it has already lost; and even in the life of today you live no more fully than in a mobile, transitory moment … Therefore, whatever includes and possesses the whole fullness of illimitable life at once and is such that nothing future is absent from it and nothing past has flowed away, this is rightly judged to be eternal, and of this it is necessary both that being in full possession of itself it be always present to itself and that it have the infinity of mobile time present [to it].
(On the Trinity) What is said of God, [namely, that] he is always, indeed signifies a unity, as if he had been in all the past, is in all the present – however that might be – [and] will be in all the future. That can be said, according to the philosophers, of the heaven and of the imperishable bodies; but it cannot be said of God in the same way. For he is always in that for him always has to do with present time. And there is this great difference between the present of our affairs, which is now, and that of the divine: our now makes time and sempiternity, as it were, running along; but the divine now, remaining, and not moving, and standing still, makes eternity. If you add ‘semper’ to ‘eternity’, you get sempiternity, the perpetual running resulting from the flowing, tireless now.
So, God’s eternity is that God’s limitless life is possessed by God all at once without the passing of the past or the anticipation of the future. This was the common definition in the medieval era.
One of the claims Stump makes elsewhere is that God’s eternity means that there is a sense in which Christ is eternally incarnate (see the last section of the review) for us.