10 Now who is he that fulfills the Law, but he that has charity? Ask the Apostle, “Charity is the fulfilling of the Law. For all the Law is fulfilled in one word, in that which is written, You shall love your neighbour as yourself.” But the commandment of charity is twofold; “You shall love the Lord your God with all your heart, and with all your soul, and with all your mind. This is the great commandment. The other is like it; You shall love your neighbour as yourself.”
They are the words of the Lord in the Gospel: “On these two commandments hang all the Law and the Prophets.” Without this twofold love the Law cannot be fulfilled. As long as the Law is not fulfilled, there is infirmity. Therefore he had two short, who was infirm thirty and eight years. What means, “had two short”? He did not fulfil these two commandments. What does it profit that the rest is fulfilled, if those are not fulfilled? Have you thirty-eight? If you have not those two, the rest will profit you nothing.
You have two short, without which the rest avail not, if you have not the two commandments which conduct unto salvation. “If I speak with the tongues of men and angels, and have not charity, I have become as sounding brass, or a tinkling cymbal. And if I know all mysteries, and all knowledge, and if I have all faith, so that I could remove mountains, and have not charity, I am nothing. And if I distribute all my substance, and if I give my body to be burned, and have not charity, it profits me nothing.” They are the Apostle's words.
All those things therefore which he mentioned are as it were the thirty-eight years; but because charity was not there, there was infirmity. From that infirmity who then shall make whole, but He who came to give charity? “A new commandment I give unto you, that you love one another.” And because He came to give charity, and charity fulfills the Law, with good reason said He, “I came not to destroy the Law, but to fulfil.” He cured the sick man, and told him to carry his couch, and go unto his house. And so too He said to the sick of the palsy whom He cured. What is it to carry our couch?
The pleasure of our flesh. Where we lie in infirmity, is as it were our bed. But they who are cured master and carry it, are not by this flesh mastered. So then, you whole one, master the frailness of your flesh, that in the sign of the forty days' fast from this world, you may fulfill the number forty, for that He has made that sick man whole, “Who came not to destroy the Law, but to fulfil.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)