I'm hoping someone can help me with this:
In this encyclical, Pope Leo XIII affirms in the first parragraph:
Venerable Brethren, Health, and Benediction.
It is sufficiently well known unto you that no small share of Our thoughts and of Our care is devoted to Our endeavour to bring back to the fold, placed under the guardianship of Jesus Christ, the Chief Pastor of souls, sheep that have strayed. Bent upon this, We have thought it most conducive to this salutary end and purpose to describe the exemplar and, as it were, the lineaments of the Church. Amongst these the most worthy of Our chief consideration is Unity. This the Divine Author impressed on it as a lasting sign of truth and of unconquerable strength. The essential beauty and comeliness of the Church ought greatly to influence the minds of those who consider it. Nor is it improbable that ignorance may be dispelled by the consideration; that false ideas and prejudices may be dissipated from the minds chiefly of those who find themselves in error without fault of theirs; and that even a love for the Church may be stirred up in the souls of men, like unto that charity wherewith Christ loved and united himself to that spouse redeemed by His precious blood. "Christ loved the Church, and delivered Himself up for it" (Eph. v., 25).
When he says, "without fault of theirs," is he speaking of material heretics (someone who in good faith does not know that what they hold to be contrary to the teaching of the Church- lets say someone who was born into Protestantism?)