John Cassian
c. A.D. 360–435
“But that even the powers above are, as we said, subject to change is shown by those who fell from their ranks through the fault of a corrupt will. This is why we should not think that the nature of those who remain in the blessed condition in which they were created is unchangeable, simply because they were not similarly led astray to choose the worse part. For it is one thing to have a nature incapable of change and another thing for a person through the efforts of his virtue, and by guarding what is good through the grace of the unchangeable God, to be kept from change. For everything that is secured or preserved by care can also be lost by carelessness. And so we read, "Call no one happy before his death," because so long as an individual is still engaged in the struggle, and if I may use the expression, still wrestling—even though he generally conquers and carries off many prizes of victory—yet he can never be free from fear and from the suspicion of an uncertain outcome. And therefore God alone is called unchangeable and good because his goodness is not the result of effort, but he possesses it naturally, and so he cannot be anything but good. No virtue then can be acquired by an individual without the possibility of change. However, in order that when it once exists it may be continually preserved, it must be guarded with the same care and diligence with which it was acquired.”