Harnack considered creeds such as the Apostles’ Creed and the Nicene Creed superfluous
to Christian practice. For him, the creeds represented theological systems (particularly
those colored by ancient Greek philosophy) wholly irrelevant to living out a life of faith.
Harnack’s book examines the Apostles’ Creed historically—its composition, how it
entered into church practice, who used it, when people used it, etc. Harnack’s perspective
and research has remained influential both in academic theology and in the practices of
many Protestant churches.