What the Incarnation Means

I am reading Frank Sheed's little book, "A Map of Life," and I am enjoying its wonderful simplicity. Within this book, I have found what is perhaps the most lucid description of the Incarnation I have ever come across:

The distinction between person and nature is not some deep and hidden thing to which philosophy only comes after centuries of study. It is, on the contary, a distinction so obvious that the smallest child who can talk at all makes it automatically. If in the half-light, he sees a vague outline that might be anything, he asks, "What is that?" If, on the other hand, he can see that it is a human being, but cannot distinguish or does not recognize the features, he asks, "Who is that?" The distinction between what and who is the distinction between nature and person....A man may then be thought of as a person - who acts - and a nature - which decides the field in which he acts. In man, there is simply one nature to one person. In Christ, there are two natures to one person...