“And we all know that for awhile Augustine went off the deep end with the Manichaean heresy. Makes me wonder about Augustine quotes that people put up.”
Well, it is good that you “wonder” about it, because it basically concedes that they say what they clearly say. (This is always a hard point whenever I quote ECFs at Catholics.) But these were all things he wrote when he was a Bishop, and during that time he also wrote against the Manicheans. Nor are the Manicheans even Protestant Predestinarians, so it has nothing to do with it anyway. The truth is Augustine never fell into Manicheans after having been a Christian. He entered the Manicheans, and then was wonderfully converted to Christianity away from their errors and sins.
Either way, the value in using Augustine against Catholics is purely in that they regard him as authoritative, since he is the “doctor of grace.” So it is strange that they do not actually agree with the doctor’s remedies.
More importantly, though, is the clearness of the passages that refutes the Catholic position, which the good “Doctor” so wonderfully expounds.
It was a heresy.