St. Justin Popovich 1894-1979
You have raised many questions and asked my opinion on various issues; whole books can be written on each of them; therefore, I have to be very brief, as brief as possible.
The attitude towards the non-orthodox Christian world, first and foremost, one must establish oneself in Orthodoxy with one’s mind and heart and life: in it’s Holy Mysteries and holy virtues; thereby catholicizing oneself, one’s mind and heart and life; living constantly with “all the saints” for this is only way to know divine-human depths and heights and breadth of everything belonging to Christ: to live “with all the saints” = to think “with all the saints” = to feel “with all the saints” = to pray “with all the saints” = to love “with all the saints”. Only in this way the holy and infallible criterion of Truth is provided = of the Church of Christ which invariably is the Hypostatic Truth of Christ the God-man, neither anyone or anything other than Him: “the fullness of Him who fills all in all.”
…”Ecumenisms” are in fashion. But, it seems to me, the most important thing therein is being overlooked: Ecumenism of the Theanthropic Truth is heart of Theanthropic Orthodox ecumenism, which invariably is the Hypostasis of the God-man Christ, in its cosmic, pan-cosmic, above-cosmic and all-embracing omneity as well as in its historical concreteness. On no account can man, or anything human, be a criterion, a symbol, or a concretum of ecumenism. Man, whoever he may be, can never be a criterion, for this but only and always the God-man. The entire tragedy of the West resides in its rejection of Christ’s God-manhood, both as modus vivendi and modus cognoscendi, through various kinds of hominisms and humanisms. (Letter Dec. 25, 1964)
Please download St Justin Popović book “The Orthodox Church and Ecumenism”.