Very good quote from His Holiness.
Indeed it is the obstinate sustained denial of the truths of the Catholic Church after they have been explained to him, — the “pertinacia”, or what I referred to as anti-Catholicism — that makes one a heretic and therefore puts his soul in danger of loss. “Cultural Protestantism” — partaking of the salvific grace of the Catholic Church through the darkened lense of a Protestant community of faith that one is naturally acculturated to, does not carry the same danger as heresy.
That is not an excuse to remain a Protestant, of course, but an important reminder that we should not lose hope for those who are separated from the Church while holding no malice toward her.