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. There was a bit of discussion going on here, but the comments got out of hand and out of order, which was a shame.
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 and here [with sample pages] and here) 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.