That picture I call "Gandalf: the incarnation", and it goes with the following text from chapter "Istari":
[Manwe]Who would go? For they must be mighty, peers of Sauron, but must forgo might, and clothe themselves in flesh so as to treat on equality and win the trust of Elves and Men. But this would imperil them, dimming their wisdom and knowledge, and confusing them with fears, cares, and wearinesses coming from the flesh.
J.R.R.Tolkien, "The Unfinished Tales"