Ehrenberg volunteered for the First World War and served as a non-commissioned officer, then a lieutenant after late 1914.
 He won the Iron Cross, 2nd Class as well as the Badische Offiziersorden (Zähringer Löwe 2.Klasse).
He left the war and army early due to reasons of health, as did many philosophers, thinkers, musicians and writers, in all armies and on all fronts.
He devoted more time to his philosophical and literary interests.

Ehrenberg had seen the war as a legitimate defensive war, but during this time and afterwards, his views changed completely.
He spoke of war crimes and German guilt.
 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.
 He began making Christian pacifist statements in 1919.
In the same year, he received an associate professorship in Heidelberg.
 At this time, working with Christian socialists, he began to think about becoming a Protestant minister.

Ehrenberg began his theological studies in Münster, in 1922, completing his second theological exam in 1924.
In 1923 and 1925, he and Nicolai von Bubnov published two volumes of German translations of Russian theological writings which were acquired and read by Dietrich Bonhoeffer and twice quoted from an essay that was in the second volume.
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.


Abandoning a promising academic career, in 1925, he became the minister of Pauluskirche in Bochum, in a heavily working-class area.
 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.
In 1927, he made speeches on church and anti-semitism in opposition to riots organised by Nazi brownshirts.
One lecture he gave in Hattingen, entitled "The Church and Anti-semitism" prompted a letter of complaint against him to the consistory in Münster:
"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.
Ehrenberg volunteered for the First World War and served as a non-commissioned officer, then a lieutenant after late 1914.  He won the Iron Cross, 2nd Class as well as the Badische Offiziersorden (Zähringer Löwe 2.Klasse). He left the war and army early due to reasons of health, as did many philosophers, thinkers, musicians and writers, in all armies and on all fronts. He devoted more time to his philosophical and literary interests.
Ehrenberg had seen the war as a legitimate defensive war, but during this time and afterwards, his views changed completely. He spoke of war crimes and German guilt.  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.  He began making Christian pacifist statements in 1919. In the same year, he received an associate professorship in Heidelberg.  At this time, working with Christian socialists, he began to think about becoming a Protestant minister.
Ehrenberg began his theological studies in Münster, in 1922, completing his second theological exam in 1924. In 1923 and 1925, he and Nicolai von Bubnov published two volumes of German translations of Russian theological writings which were acquired and read by Dietrich Bonhoeffer and twice quoted from an essay that was in the second volume. 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.

Abandoning a promising academic career, in 1925, he became the minister of Pauluskirche in Bochum, in a heavily working-class area.  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. In 1927, he made speeches on church and anti-semitism in opposition to riots organised by Nazi brownshirts. One lecture he gave in Hattingen, entitled "The Church and Anti-semitism" prompted a letter of complaint against him to the consistory in Münster:
"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.
Hans Ehrenberg