This conflict too we read in the Apostle has for our good been placed in our members: “For the flesh lusteth against the spirit: and the spirit against the flesh. But these two are opposed to each other so that ye should not do what ye would” (Gal. 5:17).

You have here too a contest as it were implanted in our bodies, by the action and arrangement of the Lord.

For when a thing exists in everybody universally and without the slightest exception, what else can you think about it except that it belongs to the substance of human nature, since the fall of the first man, as it were naturally.

And when a thing is found to be congenital with everybody, and to grow with their growth, how can we help believing that it was implanted by the will of the Lord, not to injure them but to help them?

But the reason of this conflict, that is, of flesh and spirit, he tells us is this: “that ye should not do what ye would.”

And so, if we were to fulfil what God arranged that we should not fulfil (in other words, if we were able to do what we would), how could we help believing that it would be bad for us?

And this conflict implanted in us by the arrangement of the Creator is in a way useful to us, and calls and urges us on to a higher state.

And if it ceased, most surely there would ensue on the other hand a peace that is fraught with danger.

John Cassian (c. 360-435): Conferences 4,7.