After the Second World War, he was a pioneer in Catholic-Jewish interfaith dialogue through his work at Gertrud Luckner's Freiburger Rundbrief and numerous personal correspondencies.
Although Thieme died before the end of the Second Vatican Council, his activities, along with "his intellectual sparring partner" Oesterreicher, paved the way for Nostra aetate (Declaration on the Relation of the Church with Non-Christian Religions).
As early as 1924 he received his doctorate under his teacher Hans Driesch on the subject of Schopenhauer's metaphysics in its relationship to the Kantian transcendental philosophy.
[3] Thieme continued to pronounce his religious beliefs, however, editing the Religiöse Besinning publication which promoted ecumenism between Protestants and Catholics (something then condemned by the Vatican).
While in Switzerland, Thieme was in contact with other political exiles on the left who had fled Germany, in particular Walter Benjamin and Theodore Adorno of the Frankfurt School.
"[6][7] The correspondence between the two men lasted a number of years: in 1936, during the Berlin Olympics, Thieme helped Benjamin to publish the work German People (under the pseudonym "Detlef Holz") through Vita Nova in Lucerne, which attacked the spirit of the National Socialist-era.
[8] Here from Switzerland, together with Waldemar Gurian (a Russian-Jewish convert to Catholicism) and edited by John M. Oesterreicher (an Austrian-Jewish convert to Catholicism), Thieme wrote a memorandum in 1937 entitled "The Church of Christ and the Jewish Question", which called on all Christians, but especially the Pope and the Roman Curia, to oppose contemporary anti-Jewish sentiment and to take a public position on the movement against the Jews in Germany.
[2] He spread these ideas through his work as co-editor of the Freiburger Rundbrief, a publication associated with Gertrud Luckner (an Anglo-German convert to Catholicism from Quakerism who was part of the German resistance and had spent time in the Ravensbrück concentration camp) which he had co-edited since 1948.
[2] Thieme also maintained a close correspondence with a number of Jewish figures during this time, including Martin Buber, Ernst Ehrlich (future Director of B'nai B'rith in Europe, also based in Switzerland), as well as the Rabbis of Bern and Geneva, amongst others.