This is a very helpful excerpt from Frank J. Sheed’s book, Theology for Beginnings:
“Putting it bluntly, the life of heaven requires powers which by nature we do not possess. If we are to live it, we must be given new powers. To make a rough comparison: if we wanted to live on another planet, we should need new breathing powers, which by nature our lungs have not got. To live the life of heaven, we need new knowing and lovinig powers, which by nature our souls have not got.
For heaven our natural life is not sufficient; we need supernatural life. We have it only by God’s free gift, which is why we call it grace (the word is related to gratis). Sanctifying grace will be our next topic. Everything the Church does is connected with it, and can be understood but cloudily if we do not grasp what it is.
When we come to die there is only one question that matters—have we sanctifying grace in our souls? If we have, then to heaven we shall go. There may be certain matters to be cleared, or cleansed, on the way, but to heaven we shall go, for we have the power to live there. If we have not, then to heaven we cannot go; not because we lack the price of admission, but because quite simply our soul lacks the powers that living in heaven calls for. It is not a question of getting past the gate, but of living once we are there; there would be no advantage in finding a kindly gate-keeper, willing to let us in anyhow! The powers of intellect and will that go with our natural life are not sufficient: heaven calls for powers of knowing and loving higher than our nature of itself has. We need super-natural life, and we must get it here upon earth. To die lacking it means eternal failure.
We must look at grace more closely if we are to live our lives intelligently. Two things about it must be grasped.
First: It is supernatural, it is wholly above our nature, there is not even the tiniest seed of it in our nature capable of growing, there is nothing we can do to give it to ourselves. We can have it only as God gives it, and He is entirely free in the giving. That, as we have seen, is why it is called grace; and because its object is to unite us with God, it is called sanctifying grace.
Second: Even the word supernatural does not convey how great a thing it is. It is not simply above our nature, or any created nature. It enables us to do—at our own finite level, but really—something which only God Himself can do by nature: it enables us to see God direct. That is why it is called “a created share in the life of God.” That is why those who have it are called “sons of God”: a son is like in nature to his father; by this gift we have a totally new likeness to Our Father in heaven.
Giving us this new life, God does not give us a new soul with new faculties. He inserts it, sets it functioning, in the soul we already have. By it our intellect, which exists to know truth, is given the power to know in a new way; our will, which exists to love goodness, is given the power to love in a new way.
We get the supernatural life here on earth. Not until we reach heaven will it enable us to see God face to face and love Him in the direct contact of the will. But even on earth its elevating work has begun; it gives the intellect a new power of taking hold of truth—by faith; it gives the will new powers of reaching out to goodness—by hope and by charity.
Faith, then, does not mean simply feeling that we believe more than we used to; hope does not mean simply feeling optimistic about our chances of salvation; charity does not mean simply feeling pleased with God. All three may have their effect on our feelings; but they are not feelings; they are wholly real.
The supernatural life in our souls is a new fact, as real as the natural life we have to start with. The powers it gives are facts too; they enable us to do things which without them we could not do: they are as real as eyesight, and considerably more important. Without eyesight, we could not see the material world. But without sanctifying grace we should not be able to see God direct, which is the very essence of living in heaven.
Not only that: here below we should not be sharers of the divine life, sons of God, capable already of taking hold of God by faith and hope and charity, capable of meriting increase of life. This increase of life must be realized; one can be more alive or less, and our life in heaven will differ according to the intensity of faith and hope and charity in our souls when we come to die.
We shall go on to consider these three virtues in detail. Meanwhile concentrate upon one truth: grace is not just a way of saying that a soul is in God’s favor; it is a real life, with its own proper powers, living in the soul; and he who has it is a new man. A soul with sanctifying grace in it is indwelt by God.” (Frank J. Sheed.)