44 This is our final wish, venerable brethren, that when through your diligence the memory of the sacred council of Chalcedon is celebrated, all should be urged to adhere with a most firm faith to Christ our Redeemer and our King. Let no one be deceived by the fallacies of human philosophy or led astray by the quibbles of human speech; let no one corrupt by perverse innovation or weaken by doubt the dogma confirmed at Chalcedon, namely, that there are in Christ two true and perfect natures, the divine and the human, not confused one with another, but joined together and subsisting in the one person of the Word. Let all then be joined in a close bond with the author of our salvation, who is 'the way of holy life, the truth of divine doctrine, and the life of eternal happiness' (St. Leo Serm . lxxii, I. PL . liv, 390). Let all love our restored nature in him, let them cultivate the liberty bought by him; let them cast out the folly of the aged world; let them turn with joy to the wisdom that is ignorant of old age, the wisdom of spiritual infancy.
Source: Sempiternus Rex Christus (Vatican.va)