Theophylact of Ohrid — as excerpted in the Catena Aurea on John 1:1

“(in loco.) Sabellius is overthrown by this text. For he asserts that the Father, Son, and Holy Ghost are one Person, Who sometimes appeared as the Father, sometimes as the Son, sometimes as the Holy Ghost. But he is manifestly confounded by this text, and the Word was with God; for here the Evangelist declares that the Son is one Person, God the Father another.”