In the Second Reading Paul says it is the will of God that every human being be saved.
But it is part of Christian doctrine that not all human beings are saved. Not all human beings go to heaven when they die. How could it be that an omnipotent God wills something, and yet it doesn’t happen?
Here we need to remember that heaven is more like a marriage than it is like a place.
For a human person to be in heaven is for her to be united in love to God. Now, union between God and a human person requires that each have a mind and a will, in order for there to be two to unite together. If God’s mind and will are the only ones present, then whatever there may be, it isn’t union between God and another person.
In consequence, God cannot bring about union all by himself. God can do all the work needed for union. He can offer the grace necessary for it as a gift. But if the will of a human person rejects that grace and refuses God, then even an omnipotent God can’t get union with that person. God cannot succeed in giving grace if a human person chooses to reject it.
We have to see therefore that there are some things that God wants and does not get. The will of God is that every human being be saved, but not all human beings are saved, because a human being can reject God’s grace.
But there is no frustration of God’s will as a result.
God wills to let a person’s salvation depend entirely on her—not, of course, in the Pelagian sense that she can save herself without grace, but in the sense required by the First Reading: it is up to her and her alone whether or not she refuses the saving grace of God. And if she refuses it, then because God willed to create her as a person with a will of her own, God cannot give her the grace that she will not have.
God wants lovers, not slaves. And that is why, although it is God’s will that all human beings be saved, when some are not saved, God’s will is still fulfilled, only in a different way.