Interesting that it was written by his father's lawyer on behalf of his father. Makes me wonder if this is the first contact his father has had with him since this whole thing began.
Bruce Fein and Glenn Greenwald both were both panelists on the West Coast Civil Liberties college tour last fall (http://www.yaliberty.org/tour/fall2012).
I have no doubt this ordeal has been excruciating on the elder Snowden, as he helplessly watches the international bartering for his son's life and freedom. What I find admirable, and where the emotion and strength lies, is that there isn't the slightest hint of wavering in the father's resolve--no pleading, no hand-wringing. An incredible gesture of thanks, loving commitment, and support.
I have little doubt it will impact Snowden in much the same way it did me.