When you hear this you must not entertain the notion of different natures, as certain heretics do, who think that some men indeed are of a perishing nature, others of a saving nature, but that some are so constituted that their will leads them to better or worse. But add to the words, To you it is given, if willing and truly worthy.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: ubi sup.