6 What then? What shall we say of that night? When will it be, when no one shall be able to work? It will be that night of the wicked, that night of those to whom it shall be said in the end, “Depart into everlasting fire, prepared for the devil and his angels.” But it is here called night, not flame, nor fire. Hearken, then, why it is also night. Of a certain servant He says, “Bind ye him hand and foot, and cast him into outer darkness.” Let man, then, work while he lives, that he may not be overtaken by that night when no man can work.
It is now that faith is working by love; and if now we are working, then this is the day— Christ is here. Hear His promise, and think Him not absent. It is Himself who has said, “Lo, I am with you.” How long? Let there be no anxiety in us who are alive; were it possible, with this very word we might place in perfect security the generations still to come. “Lo,” He says, I am with you always, even to the end of the world. That day, which is completed by the circuit of yonder sun, has but few hours; the day of Christ's presence extends even to the end of the world.
But after the resurrection of the living and the dead, when He shall say to those placed at His right hand, “Come, you blessed of my Father, receive the kingdom;” and to those at His left, “Depart into everlasting fire, prepared for the devil and his angels;” then shall be the night when no man can work, but only get back what he has wrought before. There is a time for working, another for receiving; for the Lord shall render to every one according to his works. While you live, be doing, if you are to be doing at all; for then shall come that appalling night, to envelope the wicked in its folds.
But even now every unbeliever, when he dies, is received within that night: there is no work to be done there. In that night was the rich man burning, and asking a drop of water from the beggar's finger; he mourned, agonized, confessed, but no relief was vouchsafed. He even endeavored to do good; for he said to Abraham, “Father Abraham, send Lazarus to my brethren, that he may tell them what is being done here, lest they also come into this place of torment.” Unhappy man! When thou were living, then was the time for working: now you are already in the night, in which no man can work.
Source: Tractates on the Gospel of John (New Advent)