From Pope Benedict’s GA talk on Leo, from March:

Aware of the historical period in which he lived and of the change that was taking place – from pagan Rome to Christian Rome – in a period of profound crisis, Leo the Great knew how to make himself close to the people and the faithful with his pastoral action and his preaching. He enlivened charity in a Rome tried by famines, an influx of refugees, injustice and poverty. He opposed pagan superstitions and the actions of Manichaean groups. He associated the liturgy with the daily life of Christians:  for example, by combining the practice of fasting with charity and almsgiving above all on the occasion of the Quattro tempora, which in the course of the year marked the change of seasons. In particular, Leo the Great taught his faithful – and his words still apply for us today – that the Christian liturgy is not the memory of past events, but the actualization of invisible realities which act in the lives of each one of us. This is what he stressed in a sermon (cf. 64, 1-2) on Easter, to be celebrated in every season of the year “not so much as something of the past as rather an event of the present”. All this fits into a precise project, the Holy Pontiff insisted:  just as, in fact, the Creator enlivened with the breath of rational life man formed from the dust of the ground, after the original sin he sent his Son into the world to restore to man his lost dignity and to destroy the dominion of the devil through the new life of grace.
This is the Christological mystery to which St Leo the Great, with his Letter to the Council of Ephesus, made an effective and essential contribution, confirming for all time – through this Council – what St Peter said at Caesarea Philippi. With Peter and as Peter, he professed: “You are the Christ, the Son of the living God”. And so it is that God and man together “are not foreign to the human race but alien to sin” (cf. Serm. 64). Through the force of this Christological faith he was a great messenger of peace and love. He thus shows us the way:  in faith we learn charity. Let us therefore learn with St Leo the Great to believe in Christ, true God and true Man, and to implement this faith every day in action for peace and love of neighbour.