Miaphysitism (μία/mia = one, φύσις/physis = nature) is the Christological dogma of the Orthodox Church, which teaches that Christ has one nature. He is both fully-God and fully-man: one nature without mixture, without confusion, and without separation of His divinity and humanity.
At the First Council of Ephesus, St. Cyril of Alexandria was chosen as the chief defender of the Orthodox Christian faith, against the Nestorians. In his defense, he stated that there is “one (μία/mia) nature of the Word of God incarnate.”
Bible Verses about Miaphysitism
Church Fathers on Miaphysitism