I'm going to be posting an interview here on RSB with the superb art historian Professor Joseph Leo Koerner later this week. In the meantime, to whet your appetites, here is Eamon Duffy reviewing Koerner's excellent The Reformation of the Image (from the LRB):
Joseph Koerner's scintillating, learned and eloquent book explores this shift [art as no longer sacred, but instead offering an alternative form of textuality, mere food for thought] by an extended investigation of the method and meaning of Cranach's Lutheran paintings, especially the monumental altarpiece he painted for Luther's own church, the Stadkirche at Wittenberg, installed there in 1547 as a memorial to the first and greatest of the reformers. Koerner sees in this altarpiece the key to a new aesthetic, which preserved art by turning it into a form of pious self-effacement, enacting its own theological redundancy by presenting itself as a mere system of useful signs, not so much an alternative as a supplement to text, a vehicle for information and affirmation of the new gospel. Emptied of emotion and of claims to transcendence, Lutheran art represented the sacred not by confronting the visible church with images of the invisible church, a company of the saints caught up in a heavenly worship (as in Catholic altarpieces such as Duccio's Maestà or van Eyck's Ghent Adoration of the Lamb), but by depicting the quotidian activities of the visible church itself.