When our first parent, father Adam, disobeyed the Divine command, the death sentence passed upon him. Therefore from the Creator's standpoint in a legal sense, he was dead although the dying process took over nine hundred years. The death sentence was consummated when Adam passed into the tomb. Our entire race was involved with Adam in this death sentence, as the Scriptures declare–"As by one man sin entered into the world and death by sin and so death passed upon all men." "As in Adam all die" (Roman 5:12; 1 Corinthians 15:22). From this view of the matter our Lord was saying, "Let the dead (the legally dead) bury their dead (the actually dead)."
It is because all were condemned to death in Adam that all will be made alive in Christ (see Romans 5:18,19). Corroborating the words of the Lord Jesus the Apostle says, "For the love of Christ constraineth us; because we thus judge that if one died for all then were all dead" (2 Corinthians 5:14). Jesus, in the laying down of His life, was giving Himself "a ransom for all" –those under the sentence of death and those who have entered into the great prison house of death, the tomb.