St. Augustine: The Damnation of the Invincibly Ignorant:

“But even the ignorance, which is not theirs who refuse to know, but theirs who are, as it were, simply ignorant, does not so far excuse any one as to exempt him from the punishment of eternal fire,

“though his failure to believe has been the result of his not having at all heard what he should believe; but probably only so far as to mitigate his punishment.

For it was not said without reason: ‘ Pour out Thy wrath upon the nations that have not known thee’

“nor again according to what the apostle says: ‘When He shall come from heaven in a flame of fire to take vengeance on them that know not God.’”

-St Augustine (Grace and Free Will 5)

That was one of St. Augustine's Retractions. He wrote an entire book admitting a lot of the teachings he taught were completely wrong although, to his defense, he did believe they were completely correct at the time he taught them. Not a lot of people have the guts to admit they were wrong but St. Augustine admitted he was wrong and I give him credit for that, although he (like other Church Doctors) was wrong on a lot of things.

Pope Pius XII, Mystici Corporis Christi (# 22), June 29, 1943.

Actually only those are to be included as members of the Church who have been baptized and profess the true faith, and who have not been so unfortunate as to separate themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed. "For in one spirit" says the Apostle, "were we all baptized into one Body, whether Jews or Gentiles, whether bond or free."[17] As therefore in the true Christian community there is only one Body, one Spirit, one Lord, and one Baptism, so there can be only one faith.[18] And therefore, if a man refuse to hear the Church, let him be considered - so the Lord commands - as a heathen and a publican. [19] It follows that those who are divided in faith or government cannot be living in the unity of such a Body, nor can they be living the life of its one Divine Spirit.