"What was read yesterday? An angel, the scripture said, descended at a certain moment into the pool, and whenever the angel descended, the waters moved; and whoever was first into the water was healed of whatever sickness he had. That was a figure of our Lord Jesus Christ who was to come.
"An angel: why? Because he himself is the angel of great counsel. At a certain moment: because the angel used to wait until the final hour, so that he might seize the day in its dying moments, and put off its decline. As often as the angel came down, the waters moved. You may be thinking: ‘Why does it not move now?’ Listen to the answer: signs are for the unbeliever, the believer has his faith.
"Whoever went down into the water first was healed of all his sickness. What does ‘first’ mean? Was it a priority of time or of dignity? It carries both meanings. The one to go down first in the order of time was healed first: that is, the Jews rather than the gentiles. The one to go down first in the order of dignity was healed first: that is, he who had the fear of God, zeal for righteousness, the grace of charity, the love of chastity. But in those days only one was saved. In those days, he alone was cured who went down first; and this was in figure. How much greater is the grace of the Church in which all those who go down into the water are saved.
"See the mystery here. Our Lord Jesus Christ came to the pool: many sick people were lying there. Yes, certainly there were many sick lying there, and only one was cured. Then he said to the man who was paralysed: ‘Go down into the water’. He replied: ‘I have no man to take me down’. See where you are baptised, see the source of your baptism. It is none other than the cross of Christ, the death of Christ. Here is the whole mystery: he suffered for you. In him you are redeemed, in him you are saved.
"‘I have no man’, he said: that is to say, ‘death came by a man, and the resurrection came by a man’. A man could not go down, could not be saved, if he did not believe that our Lord Jesus took flesh of a virgin. But he who said, ‘I have no man’, was waiting for ‘the mediator between God and man, the man Jesus’; he was expecting him of whom it is written: ‘And the Lord will send a man to save them’. And so he was found worthy to be healed, because he believed in Christ’s coming. Yet he would have been better and more perfect had he believed that he whose coming he was hoping for had already come."
Sermons on the Sacraments 2:3-7, James Walsh, S.J. (Trans.) in Edward Yarnold, S.J., The Awe-Inspiring Rites of Initiation: The origins of the R.C.I.A (2nd Ed.), Edinburgh: T&T Clark, 1994, pp110-112.