Longing in its purity is divine, longing when it longs for nothing is divine.
The moment an object of the longing arises, it becomes mundane. Longing is a pure fire that purifies, longing is a smokeless fire, a smokeless flame. But the moment it becomes attached to any object whatsoever -- worldly, otherworldly; money, meditation, God, nirvana, it doesn't matter -- any object, and the longing is no more pure, it is contaminated by the object. Then the object becomes more important than the longing itself. Then the longing is only a means, it is no more the end in itself.
And the whole effort of sannyas is to help you drop all objects of longing. Longing will not disappear -- in fact, the more objects are dropped, the more intense, the more total the longing will become, because the energy involved in the objects will be released. And there comes a moment when one is simply thirsty -- not thirsty for something, but just simply thirsty. Hungry -- not hungry for something, just a pure fire of longing. And that very pure fire consumes you, reduces you to ashes. And out of that, something new is born.