18 Moreover our Lord said to that man who said to Him:— Let me go and bury my father, and I will come to You. And our Lord said to him, Let the dead bury their dead, but go, preach the Kingdom of God. But how is this word understood by you, my beloved? Did you ever see the dead burying their dead? Or how shall a dead man arise to bury another dead man? But receive this explanation from me, that a sinner, while he is living, is dead unto God; and a righteous man, though dead, is alive unto God. For such death is a sleep, as David said, I lay down and slept, and awoke. Again Isaiah said, They that sleep in the dust shall awake. And our Lord said concerning the daughter of the chief of the synagogue, The damsel is not dead, but sleeping a slumber. And concerning Lazarus, He said to His disciples:— Our friend Lazarus has fallen asleep; but I go to waken him. And the Apostle said:— We shall all sleep, but we shall not all be changed. And again he said:— Concerning those that sleep, be not grieved.
Source: Demonstrations (New Advent)