It is a sweet thing, friendship, a dear balm, a happy and auspicious bird of calm. (Percy Bysshe Shelley, 19th century English romantic poet)
Life was never intended to be lived alone. When God brought humankind into his creation, it was a pair, perfectly matched for tending his creation and populating his world. After sin messed up the picture, human relationships became increasingly important. In addition to marriage, God brings friends into people’s experience which enriches lives immeasurably.
And Jonathan made David reaffirm his vow of friendship again, for Jonathan loved David as he loved himself (1 Samuel 20:17).