If you are interested I am trying to generate a little discussion about the identity of the Angel of the Lord in the OT, and the implications of this for our Christology over at the Coffee Bible Club blog - http://bibleandcoffee.blogspot.com/2009/05/whatever-happened-to-angel-of-lord.html .
The painting, by Caravaggio, is of that test case of one's biblical theology.
And, by the way, Bob Godfrey's biography of Calvin (John Calvin: Pilgrim and Pastor available here ( http://www.amazon.co.uk/John-Calvin-Pilgrim-Robert-Godfrey/dp/1433501325/ref=sr_1_8?ie=UTF8&s=books&qid=1242230574&sr=1-8 ) and here ( http://www.wtsbooks.com/product-exec/product_id/6220/nm/John+Calvin:+Pilgrim+and+Pastor+(Paperback) )[with sample pages] andhere - http://www.wscal.edu/bookstore/store/details.php?id=2183 ) is a cracking read. Accessible, moving, brisk, informative. Gives you a great handle on the man, his times, his rich theological reflections, and the controversies he faced.