Complex sentence: Greek Orthodox Churches are united in communion with each other and with the other Eastern Orthodox Churches by a common doctrine and a common form of worship, and they see themselves not as separate Churches but as administrative units of one single Church.
Split into simpler sentences: Greek Orthodox Churches are united in communion with each other and with the other Eastern Orthodox Churches. They hold a common doctrine and a common form of worship, and they see themselves not as separate Churches but as administrative units of one single Church.