During his tenure at Mount Mercy College, Pope John XXIII named Tavard a peritus conciliaris at Vatican II, where he also served as a consultant to the Secretariat for the Promotion of Christian Unity.
While he conceded that consolidation under one church was not feasible, he still implored theologians and lay Christians alike to discuss their views, seek as much common ground as they could find and leave it to God from there.
For example, he beseeched the Catholic brass to cease with the hundreds of years of condemnations of Martin Luther and to accord him a place of honor instead.
(Some issue arose concerning the editing of Tavard's article, but a comparison of the manuscript submitted and the printed text shows that they were identical).
Tavard predicted that within fifty years of the book's publication, women would be able to be ordained and priests would be allowed to marry.
True to his ecumenist beliefs, Tavard cited the models of Protestant churches when prescribing a remedy for the waning numbers of Catholic vocations.
He asserted that it was a civil war and that only the well-being of the people in that country should guide American policy with regard to Vietnam.