The Greeks, influenced by Plato, believed the physical world was corrupt and the spiritual world was not. There were those, influenced by Greek philosophy, who said they believed in Jesus, but they denied his true humanity. To them Jesus Christ could not have been a physical being, because all physical things are necessarily, by their very nature, corrupted. These folks became known as Gnostics.
Then there were those that took the exact opposite approach. Arius, a minister in North Africa (Alexandria, Egypt), went in the opposite direction of the Gnostics. He denied the deity of Jesus. Arius taught that Jesus, since he was a man, could not also be God. Arius' teachings had a huge impact and caused great doctrinal confusion that lasted for centuries.
A council of the Church was called in 325 AD to meet at the city of Nicea, in order to resolve the debate and confusion brought about by Arius' teachings. The result of that council was the Nicene Creed. I believe every Christian should be familiar with this important statement about the historic, orthodox faith from the early Church.
The term "creed" comes from the Latin word credo, which is the first word in ancient creeds like that of Nicea. It begins in Latin as follows "Credo in unum Deum, Patrem omnipotentem" (I believe in one God, the Father Almighty,). The word credo simply means 'I believe' and we derive our word creed from the Latin word credo. Creeds were written to answer false teachings, and as a tool to teach the people orthodoxy. All Christians should be familiar with Church history, and know the stories behind the great creeds of the Church.
Jesus is fully God, and fully man; this is the ancient doctrine of the Church and of the Bible, which was defended at Nicea. It is an essential part of Gospel. Anyone who denies these important truths has left Christianity for a false gospel.
Soli Deo Gloria,
The Nicene Creed
I believe in one God, the Father Almighty, Maker of heaven and earth, and of all things visible and invisible.
And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds; God of God, Light of Light, very God of very God; begotten, not made, being of one substance with the Father, by whom all things were made.
Who, for us men for our salvation, came down from heaven, and was incarnate by the Holy Spirit of the virgin Mary, and was made man; and was crucified also for us under Pontius Pilate; He suffered and was buried; and the third day He rose again, according to the Scriptures; and ascended into heaven, and sits on the right hand of the Father; and He shall come again, with glory, to judge the quick and the dead; whose kingdom shall have no end.
And I believe in the Holy Ghost, the Lord and Giver of Life; who proceeds from the Father and the Son; who with the Father and the Son together is worshipped and glorified; who spoke by the prophets.
And I believe one holy catholic and apostolic Church. I acknowledge one baptism for the remission of sins; and I look for the resurrection of the dead, and the life of the world to come.