Absolutely fundamental to the Christian religion is the belief that God, as the second person of the Trinity, took on human form and became man. Jesus Christ, whose incarnation we celebrate at this time, was fully divine – and also fully human.
I want to stress here that word “incarnation”, not just the nativity, so familiar from Christmas cards and Nativity plays. Yes, like all other humans he began life as an infant – but he lived and ministered as a man, a real man, fully human, with all that entails. We celebrate the incarnation explicitly at Christmas, but also constantly in the life of the Church, and especially in the Mass. At the consecration, we hear the words, “This is my body”, and on receiving communion, “Body of Christ”, to which we reply, “Amen”. But like so much in tradition, this response has shifted subtly over the millenia.The original response carried rather more punch.
In the early church, when the presbyter administered the holy communion to the faithful, saying “Corpus Christi”, the body of Christ, the response was not “Amen”, as we now have it, but “I am”. Do you see how radical that is? You -I- we- are the body of God, in our humanity.
–Fr Bernard Lynch, in From Queer to Eternity