Mystici Corporis Christi §102

¹⁰² Likewise, We must earnestly desire that this united prayer may embrace in the same ardent charity both those who, not yet enlightened by the truth of the Gospel, are still outside the fold of the Church, and those who, on account of regrettable schism, are separated from Us, who though unworthy, represent the person of Jesus Christ on earth. Let us then re-echo that divine prayer of our Savior to the heavenly Father: "That they all may be one, as thou, Father, in me, and I in thee, that they also may be one in us; that the world may believe that thou hast sent me."