“It was a heresy.”
What was? Augustine’s doctrine of grace? (Well, the RCC DOES consider it so when Protestants speak them), or the Manicheans? If the latter, what does that have to do with Augustine who did not assert any of their doctrines? If the former, why should we be at all bothered by the assertions of the RCC when we have the scripture that defends our every position? I’ll happily be a heretic with Augustine, Luther, Calvin, Knox, Spurgeon, Henry, etc. And you can keep your french-kissing Pope.
That’s not what I said. He was spouting Manicaean heresies before he was baptized by St. Ambrose, not afterwards. Look at the daily thread for St. Augustine to read the details.