This popular Passiontide hymn expresses very simply a characteristic Christian devotional response to the Incarnation. I take it that the writer meant by the first line not that this love remains unknown, but that, prior to the taking of frail flesh, it was (relatively speaking) unknown. Now, by contrast, the saving action of incarnation – to the point of crucifixion – has revealed that previously unknown love, and the effect of this revelation is to be the transformation of the loveless into the lovely.

There can be no doubt that the doctrine of the Incarnation has been taken during the bulk of Christian history to constitute the very heart of Christianity. Hammered out over five centuries of passionate debate, enshrined in the classical Christian creeds, explored and articulated in the great systematic theologies, the doctrine expresses, so far as human words permit, the central belief of Christians that God himself, without ceasing to be God, has come amongst us, not just in but as a particular man, at a particular time and place.