20 We think it of importance, Venerable Brethren, to delay a little in elucidating this document of the Roman pontiff, which was such an outstanding vindication of the Catholic faith. Firstly, against the assertion of Eutyches: 'I confess that our Lord was of two natures before their union; after their union I confess that he had only one nature' (St. Leo, Ep . xxviii, 6. PL . liv, 777), the holy bishop, not without a certain indignation, opposed the following clear statement of the luminous truth: 'I am surprised that this absurd and perverse statement should have escaped the severe reprimand of those who gave judgment . . . the Only Begotten Son of God is impiously described as being of two natures before the Incarnation and, equally wickedly to the Word made Flesh is attributed only one nature' ( Ibid .). He attacked with equal force and directness the opposite errors of Nestorius. 'It is because there was only one person in both natures, that the Son of God took flesh from the Virgin from whom he was born. And again the Son of God is said to have been crucified and been buried, because he suffered these things in the weakness of his human nature, not in the divinity itself, for through the divinity the only Begotten is co-eternal and consubstantial with the Father. Wherefore in the Creed we all confess "the only Begotten Son of God to have been crucified and buried" ' ( Ep . xxviii, 5. PL . liv, 771; cf. Augustinus, Contra Serm. Arianorum, c, 8. PL . xlii, 688).
Source: Sempiternus Rex Christus (Vatican.va)