[5] Around this time, he developed a close friendship with his cousin Franz Rosenzweig,[4] and with Eugen Rosenstock-Huessy,[6][7] Viktor von Weizsäcker, and Martin Buber.

[13] One of his cousins, Hedwig Ehrenberg, studied physics and mathematics at the University of Goettingen, where she met and later married Max Born.

Hans Ehrenberg, with Franz Rosenzweig and Eugen Rosenstock, was in regular correspondence with Louis D Brandeis through the friendship of their maternal families.

In view of Hans Ehrenberg's father's and uncles' relatives, friends and acquaintances, and their travels over the lands and voyages across the seas and oceans, the reach of his communications extended to a world-wide network in many countries in all continents.

[14] He joined the Social Democratic Party (SPD) in 1918, and for 18 months, was a city councilman in Heidelberg, as well as a member of workers' and soldiers' committees.

[16] He attended the World Conference of Life and Work in Stockholm, in 1925, and became friends with Nathan Soderblom and the English ecumenist George Bell.

With Eugen Rosenstock-Huessy he was a co-founder, and also a prolific member of the philosophical discussion group and journal, "Die Kreatur", during the time 1925 to 1930.

He got involved in the Kampfbund christlicher Arbeiter (The Fighting Christian Workers), though he left the SPD, feeling that parish work was incompatible with political party activism.

One lecture he gave in Hattingen, entitled "The Church and Anti-semitism" prompted a letter of complaint against him to the consistory in Münster:[1]"We cannot believe that a governing body of our Church approves of a race-conscious Jew who, as a Protestant clergyman, lectures German Protestant Christians about political anti-semitism based on racial attitudes.

In July 1933, he published 72 Leitsätze zur judenchristlichen Frage (Seventy-Two Theses to the Jewish-Christian Question), clearly stating his own opposition to antisemitism and calling on the Protestant church to do the same.

[19] After he was the target of attacks in Der Stürmer, and facing pressure from the German Christian church authorities, Ehrenberg asked for early retirement in 1937.

[4] Even though Ehrenberg was strictly anti-communist, his life was saved on several occasions by a communist trade union leader,[22] in the Sachsenhausen concentration camp.

Ehrenberg spoke openly about the German confessional church in England in an effort to prevent the growing disaster in Germany.

[citation needed] In Ehrenberg's honor and memory, the secondary school administered by the Protestant church in the Bielefeld neighborhood of Sennestadt was renamed the Hans-Ehrenberg-Schule in 1963.