Joseph’s standing figure is dominant. A key dangles from his belt, perhaps symbolic of his role over the nascent Church present in the Child. He opens a food container with his teeth and extends a canteen toward the nursing Virgin. The canteen is central to the composition and Mary gazes upon it. Joseph is the needed Nourisher of the Lord: the water he provides Mary is necessary for her to be able to nurse Jesus. By extension it may be said that through Mary Joseph serves the entire Church. See Carolyn C. Wilson, St. Joseph in Italian Renaissance Society and Art, pp. 65-7.