7 Therefore let us now see the sacred mystery whereby this impotent man is healed by the Lord. The Lord Himself came, the Teacher of love, full of love, “shortening,” as it was predicted of Him, “the word upon the earth,” and showed that the law and the prophets hang on two precepts of love. Upon these hung Moses with his number forty, upon these Elias with his; and the Lord brought in this number in His testimony. This impotent man is healed by the Lord in person; but before healing him, what does He say to him?
“Will you be made whole?” The man answered that he had not a man to put him into the pool. Truly he had need of a “man” to his healing, but that “man” one who is also God. “For there is one God, and one Mediator between God and man, the man Christ Jesus.” He came, then, the Man who was needed: why should the healing be delayed? “Arise,” says He; “take up your bed, and walk.” He said three things: “Arise, Take up your bed, and Walk.” But that “Arise” was not a command to do a work, but the operation of healing.
And the man, on being made whole, received two commands: “Take up your bed, and Walk.” I ask you, why was it not enough to say, “Walk?” Or, at any rate, why was it not enough to say, “Arise”? For when the man had arisen whole, he would not have remained in the place. Would it not be for the purpose of going away that he would have arisen? My impression is, that He who found the man lacking two things, gave him these two precepts: for, by ordering him to do two things, it is as if He filled up that which was lacking.
Source: Tractates on the Gospel of John (New Advent)