He was a leader in the anti-Nazi movement, the so-called Jungreformatorischen Bewegung, in the Kirchenkampf as a part of the Deutschen Evangelischen Kirche (DEK) in Nazi Germany.
In 1946 Ruprecht published the famous speech by Martin Niemöller about the war guilt of the Germans.
He published renowned theological encyclopedia, teaching material and published the first complete commentary series of the old testament in German (das Alte Testament Deutsch ATD) and the additional series ATD-Apokryphen.
He received the Bundesverdienstkreuz, a high honor by the German government and was the first honorary citizen of the Georg-August-Universität Göttingen.
For his 100th birthday he received an honorary doctorate by the theological faculty of this University on February 15, 1998.