Summa Theologica, by St. Thomas Aquinas, , at sacred-texts.com
We now consider the book of life; concerning which there are three points of inquiry:
(1) What is the book of life?
(2) Of what life is it the book?
(3) Whether anyone can be blotted out of the book of life?
Objection 1: It seems that the book of life is not the same thing as pre-destination. For it is said, "All things are the book of life" (Ecclus. 4:32)---i.e. the Old and New Testament according to a gloss. This, however, is not predestination. Therefore the book of life is not predestination.
Objection 2: Further, Augustine says (De Civ. Dei xx, 14) that "the book of life is a certain divine energy, by which it happens that to each one his good or evil works are recalled to memory." But divine energy belongs seemingly, not to predestination, but rather to divine power. Therefore the book of life is not the same thing as predestination.
Objection 3: Further, reprobation is opposed to predestination. So, if the book of life were the same as predestination, there should also be a book of death, as there is a book of life.
On the contrary, It is said in a gloss upon Ps. 68:29, "Let them be blotted out of the book of the living. This book is the knowledge of God, by which He hath predestined to life those whom He foreknew."
I answer that, The book of life is in God taken in a metaphorical sense, according to a comparison with human affairs. For it is usual among men that they who are chosen for any office should be inscribed in a book; as, for instance, soldiers, or counsellors, who formerly were called "conscript" fathers. Now it is clear from the preceding (Q, A) that all the predestined are chosen by God to possess eternal life. This conscription, therefore, of the predestined is called the book of life. A thing is said metaphorically to be written upon the mind of anyone when it is firmly held in the memory, according to Prov. 3:3: "Forget not My Law, and let thy heart keep My commandments," and further on, "Write them in the tables of thy heart." For things are written down in material books to help the memory. Whence, the knowledge of God, by which He firmly remembers that He has predestined some to eternal life, is called the book of life. For as the writing in a book is the sign of things to be done, so the knowledge of God is a sign in Him of those who are to be brought to eternal life, according to 2 Tim. 11:19: "The sure foundation of God standeth firm, having this seal; the Lord knoweth who are His."
Reply to Objection 1: The book of life may be understood in two senses. In one sense as the inscription of those who are chosen to life; thus we now speak of the book of life. In another sense the inscription of those things which lead us to life may be called the book of life; and this also is twofold, either as of things to be done; and thus the Old and New Testament are called a book of life; or of things already done, and thus that divine energy by which it happens that to each one his deeds will be recalled to memory, is spoken of as the book of life. Thus that also may be called the book of war, whether it contains the names inscribed of those chosen for military service; or treats of the art of warfare, or relates the deeds of soldiers.
Hence the solution of the Second Objection.
Reply to Objection 3: It is the custom to inscribe, not those who are rejected, but those who are chosen. Whence there is no book of death corresponding to reprobation; as the book of life to predestination.
Reply to Objection 4: Predestination and the book of life are different aspects of the same thing. For this latter implies the knowledge of predestination; as also is made clear from the gloss quoted above.
Objection 1: It seems that the book of life does not only regard the life of glory of the predestined. For the book of life is the knowledge of life. But God, through His own life, knows all other life. Therefore the book of life is so called in regard to divine life; and not only in regard to the life of the predestined.
Objection 2: Further, as the life of glory comes from God, so also does the life of nature. Therefore, if the knowledge of the life of glory is called the book of life; so also should the knowledge of the life of nature be so called.
Objection 3: Further, some are chosen to the life of grace who are not chosen to the life of glory; as it is clear from what is said: "Have not I chosen you twelve, and one of you is a devil?" (Jn. 6:71). But the book of life is the inscription of the divine election, as stated above (A ). Therefore it applies also to the life of grace.
On the contrary, The book of life is the knowledge of predestination, as stated above (A). But predestination does not regard the life of grace, except so far as it is directed to glory; for those are not predestined who have grace and yet fail to obtain glory. The book of life altogether is only so called in regard to the life of glory.
I answer that, The book of life, as stated above (A), implies a conscription or a knowledge of those chosen to life. Now a man is chosen for something which does not belong to him by nature; and again that to which a man is chosen has the aspect of an end. For a soldier is not chosen or inscribed merely to put on armor, but to fight; since this is the proper duty to which military service is directed. But the life of glory is an end exceeding human nature, as said above (Q, A). Wherefore, strictly speaking, the book of life regards the life of glory.
Reply to Objection 1: The divine life, even considered as a life of glory, is natural to God; whence in His regard there is no election, and in consequence no book of life: for we do not say that anyone is chosen to possess the power of sense, or any of those things that are consequent on nature.
From this we gather the Reply to the Second Objection. For there is no election, nor a book of life, as regards the life of nature.
Reply to Objection 3: The life of grace has the aspect, not of an end, but of something directed towards an end. Hence nobody is said to be chosen to the life of grace, except so far as the life of grace is directed to glory. For this reason those who, possessing grace, fail to obtain glory, are not said to be chosen simply, but relatively. Likewise they are not said to be written in the book of life simply, but relatively; that is to say, that it is in the ordination and knowledge of God that they are to have some relation to eternal life, according to their participation in grace.
Objection 1: It seems that no one may be blotted out of the book of life. For Augustine says (De Civ. Dei xx, 15): "God's foreknowledge, which cannot be deceived, is the book of life." But nothing can be taken away from the foreknowledge of God, nor from predestination. Therefore neither can anyone be blotted out from the book of life.
Objection 2: Further, whatever is in a thing is in it according to the disposition of that thing. But the book of life is something eternal and immutable. Therefore whatsoever is written therein, is there not in a temporary way, but immovably, and indelibly.
Objection 3: Further, blotting out is the contrary to inscription. But nobody can be written a second time in the book of life. Neither therefore can he be blotted out.
On the contrary, It is said, "Let them be blotted out from the book of the living" (Ps. 68:29).
I answer that, Some have said that none could be blotted out of the book of life as a matter of fact, but only in the opinion of men. For it is customary in the Scriptures to say that something is done when it becomes known. Thus some are said to be written in the book of life, inasmuch as men think they are written therein, on account of the present righteousness they see in them; but when it becomes evident, either in this world or in the next, that they have fallen from that state of righteousness, they are then said to be blotted out. And thus a gloss explains the passage: "Let them be blotted out of the book of the living." But because not to be blotted out of the book of life is placed among the rewards of the just, according to the text, "He that shall overcome, shall thus be clothed in white garments, and I will not blot his name out of the book of life" (Apoc. 3:5) (and what is promised to holy men, is not merely something in the opinion of men), it can therefore be said that to be blotted out, and not blotted out, of the book of life is not only to be referred to the opinion of man, but to the reality of the fact. For the book of life is the inscription of those ordained to eternal life, to which one is directed from two sources; namely, from predestination, which direction never fails, and from grace; for whoever has grace, by this very fact becomes fitted for eternal life. This direction fails sometimes; because some are directed by possessing grace, to obtain eternal life, yet they fail to obtain it through mortal sin. Therefore those who are ordained to possess eternal life through divine predestination are written down in the book of life simply, because they are written therein to have eternal life in reality; such are never blotted out from the book of life. Those, however, who are ordained to eternal life, not through divine predestination, but through grace, are said to be written in the book of life not simply, but relatively, for they are written therein not to have eternal life in itself, but in its cause only. Yet though these latter can be said to be blotted out of the book of life, this blotting out must not be referred to God, as if God foreknew a thing, and afterwards knew it not; but to the thing known, namely, because God knows one is first ordained to eternal life, and afterwards not ordained when he falls from grace.
Reply to Objection 1: The act of blotting out does not refer to the book of life as regards God's foreknowledge, as if in God there were any change; but as regards things foreknown, which can change.
Reply to Objection 2: Although things are immutably in God, yet in themselves they are subject to change. To this it is that the blotting out of the book of life refers.
Reply to Objection 3: The way in which one is said to be blotted out of the book of life is that in which one is said to be written therein anew; either in the opinion of men, or because he begins again to have relation towards eternal life through grace; which also is included in the knowledge of God, although not anew.