Anti-pelagian Writings by St. Augustine
Chapter 13 [VII.]--Temptation the Condition of Man.
If, then, there were no other proofs, this Lord's Prayer alone would be sufficient for us on behalf of the grace which I am defending; because it leaves us nothing wherein we may, as it were, glory as in our own, since it shows that our not departing from God is not given except by God, when it shows that it must be asked for from God. For he who is not led into temptation does not depart from God. This is absolutely not in the strength of free will, such as it now is; but it had been in man before he fell. And yet how much this freedom of will availed in the excellence of that primal state appeared in the angels; who, when the devil and his angels fell, stood in the truth, and deserved to attain to that perpetual security of not falling, in which we are most certain that they are now established. But, after the fall of man, God willed it to pertain only to His grace that man should approach to Him; nor did He will it to pertain to aught but His grace that man should not depart from Him.