Paul Tillich is the third with Barth and Bultmann as the trias of the greatest German theologians of the 20th century.
Tillich wrote about Schelling for his master and for his PhD. He was embedded in the Fichte Renaissance and the Schelling renaissance of the 1901, and it shows in his academic work. Tillich was both a theological and philosophical teacher.
Adorno was Tillich's assistant, and wrote his habilitation on Kierkegaard there. 1933 Tillich was one of the first non-Jewish suspended professors, and he emigrated into the USA upon Max Horckheimer's suggestion.
Tillich taught at Columbia and at the Union Theological Seminary, then at Harvard, then at Chicago. He wrote his Systematic Theology first in the USA.
Tillich felt that he was living on the boundary, as he indicated in his autobiography (1936).
Tillich almost re-encoded in Dynamics of Faith and Mut zum Sein the existing Christian symbolism into a new form.
Tillich expresses the tension between religion and modernity. He experienced the radicalization of the saddle time in the 1900s; the Enlightenment was the separation point for Old and New Protestantism; societal differentiation at the end of the 19th century shows this development line.
Semler and Schleiermacher opened up the question of what the religion is at the very end of the 18th century. Mechanization and industrialization was then the key issues for the end of the 19th century.
Tillich already wrote about religion in tension with the modernity just before WW1's end. Religion is a depth dimension of culture. Religion becomes a habitus within the culture. Religion stops being substantive or fixated, religion is a happening inside a culture.