If we think again of the health of the human body in order to find illustrations of what can happen in the Mystical Body, we shall be struck with another point. It is possible for a body to be free from disease, and yet to lack strength. Suppose a man has had an operation because of some disease: let us suppose further that the operation is perfectly successful so that, after it, he is free from the disease. Nevertheless he will need convalescence before his health is again perfect. For his disease has left an effect of weakness which natural forces will eliminate.
It is similar in the Mystical Body. Even after a diseased member is cured of sin by the sacrament of penance there remain some after-effects. There is what is called the “disposition to sin”; also there may well be a debt of punishment due after the guilt of the sin has been removed. The soul is not a perfect soul, even though it be free from the disease of sin and in possession of the life of grace. There is still weakness.
And just as the natural weakness of the body, after the actual cure of disease, needs to be eliminated by natural means such as rest, careful nursing, good food, plentiful sleep — so also supernatural weakness of the soul, after the cure from the guilt of sin, needs to be eliminated by the action of supernatural means before that soul can be considered a perfect soul.
– Clifford Howell, S.J. Of Sacraments and Sacrifice (1952)