From Miroslav Volf, Free of Charge (2005) at page 14:
In his new book, Volf puts it this way: Luther used the image of the conduit: We are channels of God’s gifts to our neighbors. The image is good except that a conduit merely conveys goods and does not benefit from them. We, on the other hand, benefit from the goods as well as bestow them on others. Which is to say that we don’t just receive the gifts, but we are constituted and changed by them.”