 He was a member of the Nazi party from 1930 onwards, and from 1933 onwards an active member of the German Christians and prospered as a state-antisemitism supporting theologian and professor for "ethnic theology".In 1939, he was made head of the newly founded Instituts zur Erforschung jüdischen Einflusses auf das deutsche kirchliche Leben in Jena, which was meant to serve state anti-semitism by the "Entjudung" (dejudifying) of the Bible and giving anti-Semitic theological training and arguments for Nazi propaganda.Despite his past Nazi activities, Grundmann regained some prestige as an evangelic theologian in East Germany; in 1959 he published his comments on the Gospels, which by the 1980s had become standard popular literature.