6 Wherefore have I said all this? That ye, brethren, may understand what was most excellently said by the Lord Jesus Christ, “My Father works even hitherto.” In that He does not abandon the creature which He made. And He said, “As He works, so do I also work.” In this He at once signified that He was equal with God. “My Father,” says He, “works hitherto, and I work.” Their carnal sense touching the rest was troubled. For they thought that the Lord being wearied rested, that He should work no more.
They hear, “My Father works even hitherto:” they are troubled. “And I work:” He has made Himself equal with God: they are troubled. But be not alarmed. The water is troubled, now the sick man is to be cured. What means this? Therefore are they troubled, that the Lord may suffer. The Lord does suffer, the precious Blood is shed, the sinner is redeemed, grace is given to the sinner, to him that says, “Wretched man that I am, who shall deliver me from the body of this death? The grace of God, through Jesus Christ our Lord.” But how is he cured?
If he step down. For that pool was so made, that men should go down, and not come up to it. For there might be pools of such a kind, so constructed, that men must go up to them. But why was this made in such a way that men must go down to it? Because the Lord's Passion searches for the humble. Let the humble go down, let him not be proud, if he wishes to be cured. But why was it but “one”? Because the Church is only One throughout the world, unity is saved. When then one is made whole, unity is signified. By one understand unity. Depart not then from unity, if you would not be without a part in this saving cure.
Source: Sermons on Selected Lessons of the New Testament (New Advent)