St. Athanasius said:
It is necessary for eternal salvation that one also faithfully believe that our Lord Jesus Christ became flesh.
For this is the true faith that we believe and confess: That our Lord Jesus Christ, God's Son, is both God and man.
He is God, begotten before all worlds from the being of the Father, and he is man, born in the world from the being of his mother --
existing fully as God, and fully as man with a rational soul and a human body;
equal to the Father in divinity, subordinate to the Father in humanity.
Although he is God and man, he is not divided, but is one Christ.
He is united because God has taken humanity into himself; he does not transform deity into humanity.
He is completely one in the unity of his person, without confusing his natures.
For as the rational soul and body are one person, so the one Christ is God and man.