It struck me today at Mass that the Annunciation was the first revelation of the Trinity. Mary said to the angel, 'But how can this come about, since I am a virgin?' 'The Holy Spirit will come upon you,' the angel answered, 'and the power of the Most High will cover you with its shadow. And so the child will be holy and will be called Son of God.' (Luke 1:34-5.) Mary was puzzled. Not surprisingly, because she would have assumed a child would come about in the normal way. But the answer to her puzzlement is nothing less than the doctrine of the Trinity: the Father – the Holy Spirit – the Son of God. It is a doctrine that changes everything.