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The Eternity of God
Having discussed the Divine immensity in its relation to space, we must now consider God's eternity in relation to time. Without it we can have no conception of Providence, whose decrees are eternal.
Let us examine the wrong notion people sometimes have of this Divine eternity, and then we shall better understand the true definition of it, which is likewise a very beautiful one.
What is eternity?
There is a partially erroneous conception of the Divine eternity current among those who are content to define it as a duration without beginning and without end, thinking of it vaguely as time without limit either in the past or in the
Such a notion of eternity is inadequate: because a time that had no beginning, no first day, would always be, nevertheless, a succession of days and years and centuries, a succession embracing a past, a present, and a future. That is not eternity at all. We might go back in the past and number the centuries without ever coming to an end, just as in thinking of the time to come we picture to ourselves the future acts of immortal souls as an endless series. Even if time had no beginning, there would still have been a succession of. varying moments.
The present instant, which constitutes the reality of time, is an instant fleeting between the past and the future ("nunc fluens," says St. Thomas), an instant fleeting like the waters of a river, or like the apparent movement of the sun by which we count the days and the hours. What, then, is time? As Aristotle says, it is the measure of motion, more especially of the sun's motion, or rather that of the earth around the sun, the rotation of the earth on its axis constituting one day as its revolution around the sun constitutes one year. If the earth and the sun had been created by God from all eternity and the regular motion of the earth around the sun had been without beginning, there would not have been a first day or a first year, but there would always have been a succession of years and centuries. Such a succession would then have been a duration without either beginning or end, but a duration, nevertheless, infinitely inferior to eternity; for there would always have been the distinction between past, present, and future. In other words, multiply the centuries by thousands and thousands, and it will always be time; however long drawn out, it will never be eternity.
If, then, to define the Divine eternity as a duration without either beginning or end is inadequate, what is it? The answer of theology is that it is a duration without either beginning or end, but with this very distinctive characteristic, that in it there is no succession either past or future, but an everlasting present. It is not a fleeting instant, like the passing of time, but an immobile instant which never passes, an unchanging instant. It is "the now that stands, not that flows away," says St. Thomas (Ia, q. 10, a. 2, obj. la), like a perpetual morning that had no dawn and will know no evening. How are we to conceive this unique instant of an unchanging eternity? Whereas time, this succession of days and years, is the measure of the apparent motion of the sun or the real motion of the earth, eternity is the measure or duration of the being, thought, and love of God. Now these are absolutely immutable, without either change or variation or vicissitude. Since God is of necessity the infinite fulness of being, there is nothing for Him to gain or to lose. God can never increase or diminish in perfection; He is perfection itself unchangeable.
This absolute fixity of the Divine being necessarily extends to His wisdom and His will; any change or progress in the Divine knowledge and love would argue imperfection.
The unchangeableness, however, is not the unchangeableness of inertia or death; it is that of supreme life, possessing once and for all everything it is possible and right that it should possess, neither having to acquire it nor being able to lose it.
Thus we come to the true definition of eternity: an exceedingly profound and beautiful definition, one full of spiritual instruction for us.
Boethius, in his Consolations of Philosophy, formulated what has continued to be the classical definition: Aeternitas est interminabilis vitae tota simul et perfecta possessio ("eternity is the simultaneous possession in all its perfection of endless life"). It is the uniformity of changeless life, without either beginning or end, and possessed wholly at once. The principal phrase in the definition is tota simul ("wholly at once"). The unique distinction of the Divine eternity is not that it is without beginning or end, but that it is without change, so that God possesses His infinite life wholly at once. Plato says that time is the mobile image of an immobile eternity, so far, at any rate, as it is possible for a passing instant to be the image of an instant that does not pass.
Time, too, with its succession of moments has often been compared to the foot of a lofty mountain the summit of which represents the unique instant of eternity. From the summit of this eternity of His, God sees in a single glance the whole series of generations succeeding one another in time, as a man from the top of a mountain can see in one glance all who pass on their way in the valley below. Thus the unique, unvarying instant of eternity corresponds to each successive moment of time, the moments of our birth and death included. Time is thus, as it were, the small change in the currency of eternity.
What characterizes time is change or motion, which is measured by time. The distinctive characteristic of eternity is that unchangeable instant in which God possesses His infinite, endless life wholly at once. 
Here on earth we have not, when born, the fullness of life. In childhood we have not yet the vigor of youth or the experience that comes with age; and then, when we reach maturity, we no longer possess the freshness of childhood or the readiness of youth. Not only is this true of our life as a whole, but we do not possess one year of it all at once. The year has its changing seasons, so that what summer brings, winter denies. The same must be said of the weeks and the days. Our life is distributed: hours of prayer are distinct from hours of work, and these again from hours of rest and recreation. Just as we do not hear the whole of a melody at once, so it is with our life: its events happen in succession.
On the other hand, it is said of Mozart that he was eventually able to hear a melody not as something continuous, in the way other listeners do, but all at once, in the law that gave it birth. In composing the opening bars of a melody, he foresaw and in some way heard its finale. To hear a melody all at once is a faint image of that Divine eternity in which God possesses His infinite life of thought and love simultaneously and without any succession. In the life and thought of God it is impossible for Him to distinguish between a before and an after, a past and a future, a childhood, youth, and maturer age.
We have another faint image of the Divine eternity in a great scholar who spends long years in studying successively all the branches of a particular science, and eventually is able to view them all in the general principles governing the science, in the master idea from which the other ideas are successive developments. Thus Newton must have seen the various laws of physics as consequences of one supreme law; and at the end of his life St. Thomas saw somewhat at a glance the whole of theology as contained in a few general principles.
Another and closer image of the Divine eternity is to be found in the soul of a Saint who has reached a life of almost continuous union with God; he has now risen beyond the vicissitudes and flight of time. The Saint, too, has his hours of work as well as of prayer, but even his work is a prayer; and because in the summit of his soul he remains in almost continuous union with God, he possesses his life in a manner "all at once"; instead of dividing and dissipating his life, he unifies it.
The eternity of God, then, is the duration of a life that not only had no beginning and will have no end, but that is absolutely unchangeable and consequently wholly present to itself in an instant that never passes. In one absolute unfleeting "now" it condenses in a transcendent manner all the varying moments that succeed one another in time.
With men, captivated as they are by sense, an unchangeable eternity has the appearance of death; for their idea of immobility is that of inertia and nothing more; it does not extend to that immobility which comes from a fulness of life so perfect that any progress in it is unthinkable.
It follows that the divine thought, since its measure is eternity, embraces in a single glance all time, every succeeding generation, every age. In a single glance it sees the centuries preparing for the coming of Christ and thereafter, reaping the benefits of that coming. In that same unique glance, the Divine thought sees where our souls will be in a hundred, two hundred, a thousand years to come, and forever. If only this truth were kept in mind, many objections against providence would vanish. The true notion of providence is, as it were, the resultant of the contemplation of those Divine perfections which it presupposes.
As the thought of God is unchangeable, so also is His love. With no shadow of change in itself, it summons souls into existence at the moment it has fixed from all eternity. From all eternity love pronounces a free fiat to be freely realized in time. At the appointed time the soul is created, justified in Baptism or by conversion, receives a multitude of graces and in the end, if no resistance is offered, that grace of a happy death by which it is saved. The created effect is new, not so the Divine act producing it: Est novitas effectus absque novitate actionis, says St. Thomas. The Divine action is eternal, but produces its effect in time and when it wills.
On the heights of eternity God remains unchanging; but beneath Him all is change, save only those souls who cleave unalterably to Him and so share in His eternity.
Eternity and the value of time
What is the spiritual lesson for us in this Divine perfection of eternity? The great lesson to be learnt is that union with God on earth brings us near to eternity. It also makes clearer to us the full value of the time allotted us for our journey: a bare sixty or eighty years, an exceedingly short span on which depends an eternity, the briefest of prefaces to an endless volume.
The thought of eternity brings home to us especially the high value we should place on the grace of the present moment. For the proper performance of our duty at any given instant we require a particular grace, the grace we ask for in the Hail Mary: "Holy Mary, Mother of God, pray for us sinners now and at the hour of our death. Amen." Pray for us sinners now. Here we beg for those special graces, varying with each moment, which enable us to cope with our duties in the course of the day and reveal to us the importance of all those trivial things that bear some relation to eternity. Although, as we utter the word "now," we are often full of distractions, Mary as she listens is all attention. She receives our prayer gladly, and forthwith the grace we need at the moment to persevere in our prayer, in suffering, in whatever we are doing, comes down to us, even as the air we breathe enters our breast. As the present minute is passing, let us remember that the body and its sensibilities, alternating between joy and sadness, are not the only realities; there is also our spiritual soul, with the influence Christ has upon it, and the indwelling of the three Persons of the Blessed Trinity. Whereas the superficial and light minded have a horizontal view of things, seeing material things and the life of the soul from the same plane of every fleeting time, the saints have unceasingly a perpendicular view of things; they see them from above and penetrate their depths, contemplating God at the summit of them all. The thought of eternity is the standard by which they estimate the value of time, past, present, and to come, and thus their judgments are gradually brought to the true focus.
Following their example, let us abandon to infinite mercy the whole of our life, both past and future. In a very practical way, inspired by faith, let us live the life of the present moment. In this fleeting now, be it dull or joyful or fraught with pain, let us see a faint image of the unique instant of changeless eternity; and because of the actual grace it brings us, let us see in it also a living proof of the fatherly kindness of God.
In this spirit let us go forward in the power of our Lord Who in the Sacrifice of the Mass never ceases to offer Himself for us by an ever-living interior oblation in His heart, an oblation that transcends time as does the vision that hallows His holy soul.
Walking thus, we draw close to that eternity which we are some day to enter. In what will this entry into glory consist? We shall receive eternal life, which will consist in seeing God as He sees Himself. It will be an intuitive vision, never interrupted by either slumber or distraction, an unchanging vision of the self-same infinite object, which will be of inexhaustible profundity for us. This vision will be succeeded by a love for God equally changeless, which nothing can ever destroy or diminish. This vision and love will no longer be measured by time, but by a participated eternity. Although they are to have a beginning, they will henceforth be without end, without change of any kind, without before or after; the instant which is to be the measure of our beatific vision will be the unique instant of changeless eternity.
We are given an inkling of what this means, when, in the contemplation of some lofty truth or at prayer, we are so absorbed at times that we no longer take account of the passing hours. If such is our occasional experience, what will it be in the future life, which is not only future but is rightly called eternal, since it will no longer be measured by time but by eternity, which is the measure of the simultaneous being and life of God? Then we, too, shall possess all our love at once instead of seeing it languish, wavering between lukewarmness and a passing fervor, all our knowledge at once and no longer piecemeal.
Let us end with this thought from St. Augustine: "Unite thy heart to God's eternity and thou, too, shalt be eternal; be thou united to God's eternity and there await with Him the things that pass beneath thee" (Comm. in Psalm. 91).
It is only to us that eternity is obscure; in itself it is far more luminous than fleeting time, for it is the unchangeableness of the supremely luminous knowledge and love of God.
1. Although our happiness in Heaven will have a beginning, it will be rightly called eternal life, for it will have as its measure a participated eternity. The Beatific Vision, in fact, is an ever-unchanging act, far transcending the continuous time of our earthly life, and that discrete time marking the thought succession of the Angel. This is the element of truth in Plato's allegory of the cave.