God & Reason
The Incarnation and the Hypostatic Union
In the Incarnation, the eternal Son of God assumed a complete human nature, becoming truly man while remaining truly God, one divine Person subsisting in two natures without confusion or division.
Catholic teaching
The Church teaches that at a definite point in history, the eternal Word of God, the second Person of the Trinity, took to himself a complete and individual human nature—a rational human soul and a human body—in the womb of the Virgin Mary by the power of the Holy Spirit. This union of divine and human natures in the one Person of the Word is called the hypostatic union: Christ is not a hybrid or a divine person merely appearing human, nor two persons cooperating, but one Person, fully God and fully man, each nature retaining its own proper characteristics and operations while united without confusion, change, division, or separation, as defined at the Council of Chalcedon in 451.
Biblical foundation
John states directly that 'the Word became flesh and dwelt among us,' joining in one sentence the eternal divine Word and the reality of becoming flesh. Paul's hymn in Philippians describes Christ as existing 'in the form of God' who nevertheless 'emptied himself, taking the form of a servant, being born in the likeness of men,' describing the same subject as both divine and human without ceasing to be the one Son. The angel Gabriel tells Mary that the child conceived by the Holy Spirit's overshadowing 'will be called holy, the Son of God,' locating the divine sonship in the very act of human conception.
Scripture references
Historical evidence
The Council of Ephesus (431) condemned Nestorius's teaching that seemed to divide Christ into two subjects, defining that Mary could rightly be called 'Theotokos' (God-bearer) precisely because the one she bore was one divine Person, even though his humanity came entirely from her. The Council of Chalcedon (451), drawing on Pope Leo the Great's Tome, produced the definitive Christological formula still recited today: one and the same Christ, acknowledged in two natures, without confusion, without change, without division, without separation, the distinction of natures being preserved and coming together into one Person. This precise language, forged over intense fifth-century debate, remains the universally accepted Christological standard across Catholic, Orthodox, and most Protestant Christianity.
The Church Fathers
“Each nature keeps its own properties without loss... the one being resplendent with miracles, the other subjected to injuries.”
“We do not divide the Word into two persons... but we say that the Word... having personally united to himself flesh... became man.”
“The Word of God... was made man that we might be made God.”