The phrase “communication of attributes” (in Latin, communicatio idiomatum) refers to the way in which we can say things about Christ’s person that more specifically relate to one of His natures. In other words, whatever we can say about Christ’s human nature, we can also say about His person. Whatever we can say about His divine nature, we can also say about His person.
However, here is where a difference occurs between the Reformed and the Lutheran. The Lutherans believed in a different communication than the Reformed do. The Lutherans believed that what can be said about Jesus’ divine nature can also be said about His human nature. This is how they undergird their doctrine of consubstantiation. If the attributes of God can be communicated to Christ’s human nature, then there is no obstacle to saying that Christ is physically present here on earth in, around, through, and under the elements of bread and wine.
The Reformed did not believe in this form of the communication of attributes. Instead, they believed that Christ’s human nature stayed human, and Christ’s divine nature stayed divine, and that those two natures did not communicate attributes to each other, but rather to the person of Christ. I have tried to draw a little graphic design that will help illustrate the point. The lines represent the natures of Christ, and the arrows represent the communication of attributes. Now, some who are calling themselves Reformed on this blog have been arguing for a Lutheran version of Christology. And these people have suggested that I have been undervaluing the hypostatic union of the divine and the human. As one can see from this diagram, however, the Reformed view of the communication of attributes draws one’s eye to the apex, which can be said to be the hypostatic union. So, on the contrary, the hypostatic union is what prevents us from attributing human characteristics (or suffering!) to the divine nature. The hypostatic union is precisely the point at which the inseparability and distinction of the two natures meets.