St. Leo the Great: On the two natures of Christ

 The properties of the two natures (divine and human) thus remain entire but come together in one Person: majesty is bound to humility, power to weakness, eternity to mortality. In order to be able to pay off the debt belonging to our condition, the nature inaccessible to suffering is united to that which can suffer and, as was needful in order to save us, Jesus Christ made man, the one and the same Mediator between God and man, could die in his human nature while remaining immortal in his divine nature... He has taken the form of a slave without the stain of sin, raising up humanity, without detracting from the Godhead. For this abasement, whereby the Invisible is made visible, and the Creator, the Lord of all things, have wished to become one of those subject to death, has been a condescension of His mercy, not a diminution of His power... So the Son of God has come into this world, descending from His abode in heaven but without giving up the glory of His Father; and He is born into a new order of things and by a new birth... The same Person is thus at once true God and true man; and this unity is genuine, for it comprises the humanity of man and the majesty of God... The Catholic Church lives and ever continues by this faith that, in Jesus Christ, neither the manhood without the true Godhead nor the Godhead without the true manhood is believed in.

+St. Leo the Great, from Letter 28 to St. Flavian¹, in Leo the Great Collection.
¹This letter is that which was read at the 4th Ecumenical Council in Chalcedon in 451AD.