Difference between joy and suffering becomes tenuous

From “The Grain of Wheat” by Hans Urs von Balthasar

The more we come to know God, the more the difference between joy and suffering becomes tenuous; not only do both things become engulfed in the One Will of the Father, but love itself becomes painful, and this pain becomes an irreplaceable bliss.

Purgatory: perhaps the deepest but also the most blissful kind of suffering. The terrible torture of having to settle now all the things we have dreaded a whole life long. The doors we have frantically held shut are now torn open. But all the while this knowledge: now for the first time I will be able to do it - that ultimate thing in me, that total thing. Now I can feel my wings growing; now I am fully becoming myself...

In some way this reminds me of St Francis and his teaching of perfect joy.