We often here that God is eternal, but the word “eternal” can mean more than one thing.
On the one hand, it can mean everlasting–that is, something that endures through successive moments of time with either no beginning, no end, or both.
On the other hand, it can also mean atemporal–beyond or outside of time.
Catholic teaching holds that God is eternal in the second sense, but where could you go to show that?
You could quote from Aquinas on this point, but while Aquinas is very respected, including by the Magisterium, he is not himself an agent of the Magisterium.
But here is a passage which, because it is from one of John Paul II’s general audiences, is an exercise of the Church’s Magisterium:
These facts of revelation also express the rational conviction to which one comes when one considers that God is the subsisting Being, and therefore necessary, and therefore eternal.
Because he cannot not be, he cannot have beginning or end nor a succession of moments in the only and infinite act of his existence.
Right reason and revelation wonderfully converge on this point.
Being God, absolute fullness of being, (ipsum Esse subsistens), his eternity “inscribed in the terminology of being” must be understood as the “indivisible, perfect, and simultaneous possession of an unending life,” and therefore as the attribute of being absolutely “beyond time” [General Audience of Sept. 4, 1985].
So: “his eternity . . . must be understood as . . . being absolutely ‘beyond time.'”
Also note that the definition of eternity offered here the “indivisible, perfect, and simultaneous possession of an unending life,” is the classical definition proposed by the Christian philosopher Boethius in The Consolation of Philosophy, around the year A.D. 524:
It is the common judgement, then, of all creatures that live by reason that God is eternal. So let us consider the nature of eternity, for this will make clear to us both the nature of God and his manner of knowing. Eternity, then, is the complete, simultaneous and perfect possession of everlasting life; this will be clear from a comparison with creatures that exist in time.
…for it is one thing to progress like the world in Plato’s theory through everlasting life, and another thing to have embraced the whole of everlasting life in one simultaneous present. (Boethius Consolation, V.VI.) [MORE.]
Very good. I never really researched the church’s position on this, but always loved how C.S. Lewis described it as if time was before God like a stream and He could reach out into time to miraculously alter the proceedings. It was in his book Miracles.
Also one could add that any being that is not eternal (meant as “atemporal–beyond or outside of time”) cannot be God.
This is also what St. Thomas Aquinas says as well (in a different way)
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Time implies change. If there is no change, one could argue, time is meaningless. This is does not only arise from metaphysics but from physics as well.
So: Any being that is in time is a contingent being. A contingent being can never be defined as ‘God’ in the Christian sense and the understanding of Classical Theology.The reason is that any contingent being is a mix of ‘act’ and ‘potential’, or in very oversimplified terms: what is and what could be(come).If a being has some degree of potentiality it means that it is not fully perfect, i.e. such being is lacking something.Moreover such being would need a cause, because he could not be the cause of itself.God must be ‘Pure Act’, non-contingent, hence outside of time.