The Arian Crisis
The crisis concerned the faith in the divinity of Jesus. It came to a head in A.D. 318, with the writings of Arius of Alexandria: according to Arius, the Son was begotten of the Father, came from divine substance, came into existence before the centuries, but before he was begotten, he did not exist, he is not God, only a demiurge. For Arius, Christ was created and he is the Father’s adopted son.
The crisis was serious and the majority of bishops were Arians. The error was in not accepting the revelation of the divinity of the Christ, who is God. Christ reveals to us that in God there are the Father and the Son. The patriarch of Alexandria retorted that Christ is of the same nature as the Father. This caused inflamed arguments by those who coveted power.
The response of the council of Nicea
The emperor himself convoked the Council of Nicea, which met in A.D. 325, and the pope approved of its contents. Jesus is “God of God, light of light, true God of true God, begotten not made, of the same substance with the Father.”
But the heresy continued; the Church imposed that the Creed be recited during Sunday mass, and by using nonverbal language (one inclines oneself or one kneels), one venerates the moment of the Incarnation, because the Incarnation is the moment of the meeting between God and humanity.
The celebration of Christmas
The institution in Rome, around the year 336, constitutes the liturgical translation of the cristological definition of Nicea. The celebration of Christmas makes it possible to venerate the mystery of the Incarnation and to better understand it.
Cf. I. Calabuig (Marianum)
Ignazio CALABUIG, Il culto di Maria in occidente,
In Pontificio Istituto Liturgico sant'Anselmo. Scientia Liturgica,
sotto la direzione di A.J. CHUPUNGCO, vol V,
Piemme 1998. p. 277-279