There's some interesting debate as to how the song at the end of Henry V should be interpreted. Henry commands that Non Nobis and Te Deum be sung in thanks for the English victory at Agincourt, and then sets out across the muddy, corpse-strewn field carrying the body of a young boy killed by the French. As he walks, the camera pans back to show the horrors of battle: the plain churned into bloody muck, corpses strewn about, dying horses, and the like; at one point, a weeping old woman tries to rush the king and is held back by his advisors. At the same time, the beautifully-done hymn swells in the background.
The film as a whole is so very anti-war in tone that this visualization of the climactic scene is very interesting - why combine this glorious anthem with such grim imagery?
One interpretation is that the beautiful score is a reflection of Henry's character, intended to give us some insight into his views on the subject. This would be a fairly harsh indictment of his character: we see a slaughter, and he's hearing a triumphal chorus. This doesn't seem entirely consistent with Henry's character as it's presented throughout the rest of the film, but perhaps it's intended as an additional insight that alters our view of the king. It's also been suggested that the hymn is meant more to reflect the king's religious feelings about the victory than his moral or philosophical take on it (which of course says something about him, too!)
Alternately, both the tracking shot of the field and the glorious hymn can be seen as a reflection on the way history views the events portrayed. Agincourt is generally remembered as a glorious victory, and perhaps the film is chiding us a bit for that - we view the scene from a distance and listen to joyful music, but Henry is still carrying a dead child.
In any case, Patrick Doyle's version of the hymn is quite beautiful and stirring (Doyle himself played the first soldier to begin singing in the film) and is a fitting conclusion to a pleasingly competent attempt to bring Shakespeare to the screen.