Every deed and every relationship is surrounded by an atmosphere of silence. Friendship needs no words -- it is solitude delivered from the anguish of loneliness.
Now by itself, the second sentence might seem a bit uplifting and positive; the delivered could be interpreted to mean "saved; set free; etc". And if we assume this to be true, the line does carry a poetic elegance, and a sort of social beauty. But there are two things that make me think otherwise, which I shall explore below:
Firstly, the preceding sentence in the quote already states that friendship (being a sort of deed and relationship) is covered in quietness. Now, this could be a technical and semantic division between being alone, and being lonely. On the other hand, it could be a dark interpretation of friendships, implying that we only create them to stave off the conscious knowledge or acknowledgement of our inherent solitude and isolation. And the reason why I feel it could be this dark interpretation is because:
Throughout this book of random prose, Hammarskjöld frequently mentions death, and the pain of being alive. In my untrained eyes, it's difficult to tell if the figures in his prose are literal people, or analogies for parties/countries, which wouldn't be entirely impossible, given that he was the Secretary-General to the UN for some time. But in either case, the tone isn't always positive. (The ambiguity's a bit like most poetry then...) Right in the first page is the following:
Tomorrow we shall meet,
Death and I --
And he shall thrust his sword
Into one who is wide awake.
But in the meantime how grievous the memory
Of hours frittered away.
So it hard to assume that his writings can be all positive and uplifting. But it really does make you think. Well, it certainly made me think.
A sort of in-between interpretation might go like this: Solitude is the child of Loneliness, and is thence delivered. In this case, the dark view of friendships being created out of mutually loneliness is maintained, but the interpretation of Solitude is different. Out of two people in need is a created bond, implying that the friendship between two people ONLY supports those two people, and therefore are solid against the rest of humanity and its loneliness. (IE, not just any lonely person can randomly penetrate this friendship.)
But despite whichever interpretation is taken or intended, they all have a kernel of truth about the human condition, and they maintain a poetical grace. Personally, I think that a language's poetry and prose is the only true testament to its greatness.