The Popes have ever proclaimed that all conversation with non-Catholics is rightly ordered to securing for them in true charity the ineffable blessings of Catholic unity, that they may attain salvation. (It would be tedious to repeat centuries of quotations from their writings to this effect.)
In more recent decades, ecumenical dialogue has been undertaken, not to forswear what the latest Council proclaimed - that all who, grasping that the Church is necessary for salvation, must needs enter her communion to be safe and saved - but to help smooth the way for the unity of all Christ's scattered flock, by eliminating scandals, misconceptions, age-old prejudices and misunderstandings.
(To interject some levity, it reminds one of a Catholic Frenchman in the days before the Revocation of the Edict of Nante, who, to help motivate Huguenots to convert, set up a Bank of Conversions that offered cheap loans to such persons! He claimed "It prepared the heart for the operation of grace!")
Unfortunately, Catholics have sometimes deluded themselves and others, in their anxiety to be irenic, or even in their hankering after profane novelties, by vainly papering over or falsely belittling real differences of importance between our Holy Faith and the heterodox opinions of others, thinking to salve consciences and compose disputes in an insincere manner. This tendency the Roman Pontiffs have naturally opposed. But they have been abused for doing so...
Equally unfortunately, those not of our faith have been lured by this vacillation of Catholics between the conserving acts of the Magisterium and the confusing, provoking acts of ill or well-meaning persons, into surmising that Rome, too, will bend to the winds of time and change, smoothly adapting herself to the world in practising expediency. This may all too be true at an accidental level, but not at a substantial one. The promise of infallibility and indefectability is given to the whole Church at large, as well as guaranteed in the person of Christ's Vicar, as Servant of the servants of God, the successor of St Paul as well as of St Peter, consumed with the care for all the churches, to keep them in one.
How appropriate to think of this on the very feast of the dedication of the great Basilicas of St Peter and St Paul!
Alas, far from Rome in the true sense, impertinent persons in particular have played a malign part in this deviation of ecumenism from its natural role of fostering unity, to an improper purpose of maintaining (let us be candid) elaborate talkfests to occupy and waste time, without scarcely forwarding the mission of the Church. Even non-Catholics have remarked at the scandal their Catholic dialogue partners engender: for all too often, it is the Catholics who wink at Church doctrine and say as much, being all matey and conspiratorial about it! This rightly repulses many, but confirms all outsiders in the opinion that much is dirty and unpleasant within the Ark that is the Church.
Grace, the grace of the Holy Spirit Who convicts the world of sin, justice and judgement, Who inspires the will and enlightens the intellect to chance great things and belief hard truths, must be allowed to work: but its sweet secret work may be frustrated and brought to nought by hard, proud hearts, rich only in their own conceit and doubledealing, delighting not in the truth but in dreams.
What I have written of - the deliberate change in Papal policies for the last forty-odd years to indulge in Realpolitik toward non-Catholic bodies, by accentuating immediate goals (greater mutual charity, lessening of vile bigotry) relative to discreetly advertising the ultimate intent (reception of converts into full unity) - is by many unwise persons called the "old" ecumenism, when really it is newfangled.
What is now called by its enthusiasts the "new" ecumenism, and decried by its detractors (profiteers of the "old") as totally opposed to ecumenism - exemplified by the energetic steps taken by His Holiness to embrace incoming Anglicans, according them many sweet privileges, in response it must be underlined to their heartfelt pleas for corporate reunion, having been at last revolted by the unchristian antics of their original denomination - is in fact the original, settled ecumenical policy of Rome, no different in substance to the efforts, lasting or not, made since mediæval times and before, to offer rest and peace to those willing to return to the Father of Christendom.
Both the new "old" ecumenism, and the old "new" ecumenism, are true insofar as they are rightly ordered, implicitly or explicitly, to the true goal: to unite all Christians in one faith under one shepherd, for which happy cause Our Lord Himself deigned to pray directly before His saving Passion: Ut unum sint, ad salvandas animas, ad gloriam Patris.
There is an old blessing, sometimes termed Mozarabic but cropping up in the Benedictine Office and I suspect of mainstream mediæval Latin Rite origin, given its rough rhyme:
In unitate Sancti Spiritus,
benedicat vos Pater et Filius.
This is best interpreted in the deeper sense: May we, united in the one Holy Spirit, Who is the Principium Unitatis as the Quickener of our souls and bodies, as the Lifegiver to our fellowship in the Holy Catholic, that is, rightbelieving worldwide, Church, be therefore blessed by the Father and the Son - for these Three are One. Amen.