Anti-pelagian Writings by St. Augustine
Chapter 39 [XIII.]--The Number of the Predestinated is Certain and Defined.
I speak thus of those who are predestinated to the kingdom of God, whose number is so certain that one can neither be added to them nor taken from them; not of those who, when He had announced and spoken, were multiplied beyond number. For they may be said to be called but not chosen, because they are not called according to the purpose. But that the number of the elect is certain, and neither to be increased nor diminished, -- although it is signified by John the Baptist when he says, |Bring forth, therefore, fruits meet for repentance: and think not to say within yourselves, We have Abraham to our father: for God is able of these stones to raise up children to Abraham,| to show that they were in such wise to be cut off if they did not produce fruit, that the number which was promised to Abraham would not be wanting, -- is yet more plainly declared in the Apocalypse: |Hold fast that which thou hast, lest another take thy crown.| For if another would not receive unless one should have lost, the number is fixed.