A typical and entirely consistent extension of all this blurring and alienation of the ontological character of the Church's truth is the modern movement towards the so-called "union" of the churches, and the much-vaunted priority of the "love” which unites the churches over the "dogma" which divides them. One could say that this movement was historically justified, since it often looks as if union has been accomplished on the level of a common, non-dogmatic piety —on the level of pietism. What used to divide the Church from heresy was not abstract differences in academic formulations; it was the radical break and the distance between the universality of life and illusions of life, between realizing the true life of our trinitarian prototype and subjugating this truth to fallen man's fragmentary mode of existence. Dogma "defined",. or showed the limits, while the Church's asceticism secured participation in that truth of life which defeats corruption and death and realizes the image of God in the human being.
When piety ceases to be an ecclesial event and turns into an individual moral attainment, then a heretic or even a non-Chtistian can be just as virtuous as a "Christian." Piety loses its connection with truth and its ontological content; it ceases to be related to man's full, bodily participation in the life of God—to the resurrection of the body, the change of matter into "word", and the transfiguration of time and space into the immediacy of communion. Piety is transformed into an entirely uniform manner of being religious which inevitably makes differences of "confession" or tradition relative, or even assimilates the different traditions, since they all end in the same result—the moral -improvement of human life.
Thus the differences which separate heresy from truth remain empty verbal formulations irrelevant to the reality of life and death, irrelevant even to piety. They are preserved simply as variations in religious customs and traditional beliefs, with a purely historical interest. It is therefore natural for the distinct Christian confessions to seek formal union—respecting, of course, the pluralism in religious customs and theoretical formulations—since they are already substantially assimilated in the sphere of "practical life". This is the obvious basis for the unity movement in our times—when, of course, it is not guided by much more stark sociopolitical considerations.
Sociopolitical considerations, however, have influenced church life in every age; they are the sins of our human nature which has been taken into the Church. And they are not a real danger so long as we are aware that they are sins; they do not succeed in distorting the truth and the fact of the Church. The danger of real distortion lies in heresy: when we take for truth and salvation some "improved" version of the fragmented mode of existence of fallen man. And the great heresy of our age is pietism. Pietism is a heresy in the real of ecclesiology: it undermines or actually denies the very truth of the Church, transferring the event of salvation from the ecclesial to the individual ethos, to piety divorced from the trinitarian mode of existence, from Christ's way of obedience. Pietism denies the ontological fact of salvation - the Church, life as personal coinherence and communion in love, and the transfiguration of mortal individuality into a hypostasis of eternal life.
Pietism undermines the ontological truth of the Church or totally rejects it, but without questioning the formulations of that truth. It simply disregards than, taking them as Intelectual forms unrelated to man's salvation, and abandons them to the jurisdiction of an autonomous academic theology. Pietism preserves a formal faithfulness to the letter of dogmatic formulation, but this is a dead letter, irrelevant to life and existential experience.
In that particular, this real denial of the truth of salvation differs from previous heresies. It does not reject the "definitions", the limits of the Church's truth; it simply disconnects this truth from the life and salvation of man. And this disconnection covers a vast range of distinctions and nuances, so that it is exceptionally difficult to "excommunicate" pietism, to place it beyond the bounds within which the Church's truth and unity are experienced. But this is precisely why it is perhaps the most dangerous assault on this truth and unity.
From Christos Yannaras Freedom of Morality