From The Journey of Desire:

Duty reduces the dance to a drill. It’s as if you showed up with a bouquet of flowers for your anniversary. Your wife is delighted, but then you say, “Think nothing of it, my dear. It’s my obligation.”… A woman doesn’t want to be the object of duty; she wants to be desired. So does God. Thus A. W. Tozer asserted, “God waits to be wanted.”