As an aside, the desire of union with God is an "unknowable desire" until we are enlightened by the grace of faith offered by God, which enables us to know that this union is offered...it's a good question in light of the dispute over the desire of pure human nature for God.
Back to de Lubac: He argued that saying we desire union with God in our human nature is NOT the same as saying by nature we already have the beginning of that union with God. An "infinite gap" remains between nature and grace.
It's nonsense to say God owes us grace, nor was their hypothesis very helpful. Everyone agrees that we have a desire for union with God given to us by God. At some point we have to discuss why grace is freely given and isn't owed to us. Cajetan, Garrigou-Lagrange, and others merely postponed the problem, for grace gives the desire and God would have to give grace to bring about the union. The problem of justice is one of their own making in a way.
At this point in class Dr. Miller took questions, and I asked "then how can grace perfect nature, if we don't desire God as part of nature? Wouldn't that supplant human nature?" DING DING DING.
Henri de Lubac pointed out that a thing's nature is defined especially from its end or purpose. If by nature we don't have God as our purpose, then when grace gives us this desire, human nature is fundamentally altered. Whereas St. Thomas and others explained that grace perfects nature.
On an interesting note, de Lubac writes that secularism developed because of the error of Cajetan et al. There is a split between human nature and grace. Christianity thus destroys nature, or God doesn't matter, rather than redeeming and perfecting human nature.
On another note, this is where the school of the Nouvelle Théologie gots its name. Early twentieth century thought was extremely reliant on St. Thomas, but these theologians decided to return to the sources of the Fathers and other theologians, as Thomism had been carried a bit off the rails in the fight against Modernism.
Garrigou-Lagrange accused them of creating a "new theology," one that was not in keeping with the Tradition of the Church. He wasn't wrong to criticize everything but was a bit harsh. At first...Kueng and others are Modernists through-and-through.
BTW, this in no way affects the mastery of the spiritual life put forth by Reginald Garrigou-Lagrange; his work on grace in this sense is separate.
Also BTW, pray for Kueng. He's considering assisted suicide as he suffers from Parkinson's. EEK.