I agree with his conclusion. In the past I've made my own guarded attempts at grounding the cross in the eternal intra-trinitarian personal relations. I have stated it a bit more provocatively than Joel. But I think his formulation is the least we can do. Here's his conclusion:
Even if we cannot strictly speaking say that God, in his own being “suffers,” there yet remains an eternal analogue to suffering in which the redemption of the cross is already provided for and included in the eternal offering, self-surrender and—may we even say—sacrifice among the divine Persons within the Trinity. This is what Hans Urs von Balthasar terms the “supra-suffering” of the impassible God.If you are interested in theology proper, read the entire lecture.
The Trinitarian God of Scripture, therefore, is also the God of classical theism who, as being itself and pure act, remains immutably and impassibly transcendent over creation as Trinity. It is precisely in the plentitude of the intra-Trinitarian relations that God already is passionate, loving, and responsive to his creation, even, in some sense, taking up the suffering of his creatures for their redemption. This divine weakness and vulnerability is, paradoxically, the fullness of the saving power of God, that dynamic and over-abundant love that lies beyond passibility and, indeed, beyond any shadow of turning.