God’s unerring foreknowledge is symbolized by the “Book of Life.”(586) Christ Himself said to His Apostles: “Rejoice in this, that your names are written in heaven.”(587) The “Book of Life” admits neither addition nor erasure. This does not, however, mean that a man is unable to change God’s hypothetical decree of predestination with regard to himself into an absolute one. He can do this by prayer, good works, and faithful co-operation with grace.(588) Whatever promotes our salvation is included in the infallible foreknowledge of God, and consequently also in the scope of predestination. In this sense, but in no other, can we accept the somewhat paradoxical maxim: “If you are not predestined, conduct yourself so that you may be predestined.” Sacred Scripture occasionally refers to another “Book of Life,” which contains the names of all the faithful, irrespective of their predestination. This “book,” of course, is capable of alterations. Cfr. Apoc. III, 5: “I will not blot out his name out of the book of life.”(589) Finally, there is the “Book of Reprobation,” which records the wicked deeds of men and by which the unrepentant sinners will be judged. This is the “_liber scriptus_” of the “_Dies Irae_”: “_Liber scriptus proferetur._ _In quo totum continetur._”(590) β) If the divine decree of predestination is immutable, the number of the elect must be definitively fixed. “The number [of those who are predestined to the kingdom of God] is so certain,” says St. Augustine, “that no one can either be added to or taken from them.”(591) We must distinguish between the absolute and the relative number of the predestined. God, being omniscient, knows not only the abstract number of the elect, but every individual predestined to Heaven. To us the number of the elect is wrapped in impenetrable mystery. St. Thomas justly observes: “Some say that as many men will be saved as angels fell; some, so many as there were angels left; others, in fine, so many as the number of angels who fell, added to that of all the angels created by God. It is, however, better to say that ‘God alone knows the number for whom is reserved eternal happiness,’ as the prayer for the living and the dead expresses it.”(592) Whether God will round out the number of the elect by suddenly precipitating the end of the world or by a sort of “natural selection,” is an open question. To assume the latter could hardly be reconciled with the dogma of the universality of His saving will. St. Augustine seems to favor the former.(593)