Leo, Bishop of Rome (440-461), had this to say about joining of two natures, the Divine and the Human, in the person of Christ:

"The same only-begotten, eternal Son of the eternal Father was born of the Holy Ghost and the Virgin Mary. But this birth in time has taken nothing from, and added nothing to, that divine eternal nativity...For we could not overcome [the devil], unless [God] had taken our nature and made it His own...Thus the properties of each nature and substance were preserved entire, and came together to form one person...He did not become partaker of our sins because He entered into fellowship with human infirmities. He assumed the form of a servant without the stain of sin, making the human properties greater, but not detracting from the divine...Each nature preserves its own characteristics without diminution, so that the form of a servant does not detract from the form of God."

Taken from Henry Bettenson's "Documents of the Christian Church" 2nd Ed., page 49,50