[Pope St. Leo the Great (440-461) is generally recognised as the principal Doctor of the mystery of the Incarnation in the Western Church. All know the part he played, through his legates and writings, in the Council of Chalcedon (451). Ho is also the most ancient of the great Latin Preachers, whose sermons on Church festivals are still extant. To this day, in the lessons of the second nocturn at Matins, the Roman breviary makes use of Leo’s eloquence to interpret the meaning and spirit of the various liturgical solemnities, for example, at Christmas and on the feast of the Epiphany.

St. Leo is certainly at his best when commenting on the dogmatic fact of the twofold nature, divine and human, in the one Person of Christ, which sums up the mystery of the Incarnation. True to the Western trend of theological exposition, he does not stop to weave subtle theories into the fabric of dogmatic beliof : he simply enumerates truths, but these he follows up with a wonderful wealth of practical conclusions for the everyday life of the faithful. Besides his classic work—the Tomos on the Incarnation which he sent to the Fathers of Chalcedon—St. Leo has left ten sermons which he preached in Rome on the feast of Christmas (see Migne, P. L., t. 54, col. 190-254). Each ranks as both a theological and an oratorical masterpiece.