Leo XIII on Unity in Faith

Pope Leo XIII has this to say on the subject of unity of faith as the foundation for Christian unity.

Agreement and union of minds is the necessary foundation of this perfect concord amongst men, from which concurrence of wills and similarity of action are the natural results. Wherefore, in His divine wisdom, He ordained in His Church Unity of Faith; a virtue which is the first of those bonds which unite man to God, and whence we receive the name of the faithful – “one Lord, one faith, one baptism” (Eph. iv., 5).

That is, as there is one Lord and one baptism, so should all Christians, without exception, have but one faith. And so the Apostle St. Paul not merely begs, but entreats and implores Christians to be all of the same mind, and to avoid difference of opinions: “I beseech you, brethren, by the name of our Lord Jesus Christ, that you all speak the same thing, and that there be no schisms amongst you, and that you be perfect in the same mind and in the same judgment” (I Cor. 1:10).

Such passages certainly need no interpreter; they speak clearly enough for themselves. Besides, all who profess Christianity allow that there can be but one faith. It is of the greatest importance and indeed of absolute necessity, as to which many are deceived, that the nature and character of this unity should be recognized. And, as We have already stated, this is not to be ascertained by conjecture, but by the certain knowledge of what was done; that is by seeking for and ascertaining what kind of unity in faith has been commanded by Jesus Christ.

Leo XIII: Satis Cognitum, 6.

It’s worth reading this in conjunction with what Berenike has to say about The One Thing That Matters. Unity of faith doesn’t mean that people can’t disagree over a whole range of issues (including the hot-button issue of liturgy). As Berenike puts it,

if a diocese is chiefly concerned with the salvation of souls and the glory of God, then while disagreements over liturgy will not lose their seriousness (as someone points out, “It’s all the same Mass” is exactly why every single thing about it is crucially important), and everyone in it is able to work together to that end, then the One Thing that Matters is made luminously clear by the very fact of being held in perfect accord by the (sometimes violently) disagreeing.