1 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). If those about to come back to their most loving Mother (not yet fully known, or culpably abandoned) should perceive that their return involves, not indeed the shedding of their blood (at which price nevertheless the Church was bought by Jesus Christ), but some lesser trouble and labour, let them clearly understand that this burden has been laid on them not by the will of man but by the will and command of God. They may thus, by the help of heavenly grace, realize and feel the truth of the divine saying, "My yoke is sweet and my burden light" ( Matt . xi., 30). Wherefore, having put all Our hope in the "Father of lights," from whom "cometh every best gift and every perfect gift" (Ep. James i., 17) - from Him, namely, who alone "gives the increase" (I Cor . iii., 6) - We earnestly pray that He will graciously grant Us the power of bringing conviction home to the minds of men.
Source: Satis Cognitum (Vatican.va)