In the ancient Church, and until rather recently, we genuflected at the two references to the incarnation in the Mass: at the Creed and at the Last Gospel (John 1). Why did we do this? It was explained to me that the mystery was so deep that one could only fall in silent reverence.
There are many paradoxes and seeming impossibilities in the incarnation. As mysteries they cannot be fully solved, so they claim our reverence. We genuflected in the past, and we bow today at the mention of the incarnation in the creed for it is a deep mystery.