6 For, lest you should think that by believing you are not to die according to the flesh, or lest, understanding it carnally, you should say to yourself, “My Lord has said to me, Whoso hears my words, and believes Him that sent me, is passed from death to life: I then have believed, I am not to die;” be assured that you shall pay that penalty, death, which you owe by the punishment of Adam. For he, in whom we all then were, received this sentence, “You shall surely die;” nor can the divine sentence be made void.
But after you have paid the death of the old man, you shall be received into the eternal life of the new man, and shall pass from death to life. Mean while, make the transition of life now. What is your life? Faith: “The just does live by faith.” The unbelievers, what of them? They are dead. Among such dead was he, in the body, of whom the Lord says, “Let the dead bury their dead.” So, then, even in this life there are dead, and there are living; all live in a sense. Who are dead?
They who have not believed. Who are living? They who have believed. What is said to the dead by the apostle? “Arise, you that sleepest.” But, quoth an objector, he said sleep, not death. Hear what follows: “Arise, you that sleepest, and come forth from the dead.” And as if the sleeper said, Whither shall I go? “And Christ shall give you light.” Christ having enlightened you, now believing, immediately you make a passage from death to life: abide in that to which you have passed, and you shall not come into judgment.
Source: Tractates on the Gospel of John (New Advent)