It became the center of the Eastern Orthodox Church.
Constantinople became the seat of Patriarch of Constantinople one of the four patriarchs of Orthodox Christianity (the others were the patriarchs of Alexandria, Antioch and Jerusalem). From the reign of Justinian the Great onward, the emperor , whose seat was Constantinople, were the supreme head of the Orthodox Church.
but the reason religion was like important was basically because it was these people's main control of life.
I hoped that helped??