Q. How would you respond to a non-Christian who says that when Moses and Elijah came and spoke with Jesus on the Mount of Transfiguration, this incident would fall under necromancy, which is forbidden in Deuteronomy? I know that interpretation is wrong and that the Transfiguration was not necromancy, but I wasn’t sure how to explain this.
It is true that the Law of Moses says in Deuteronomy, “Let no one be found among you … who is a medium or spiritist or who consults the dead.” But we need to understand what is being prohibited, and why.
This particular prohibition comes within a cluster of similar ones that forbid various kinds of practices by which people seek to call upon ghosts or evil spirits or other occult powers. The principle behind all these laws is that human beings need to respect their own finiteness and not try to draw upon other powers to get what they want. They need to respect the boundaries between life and death, good and evil, and humanity and the spirit world. Rather than seeking to get whatever information or results they want by calling on other powers, they need to live in fellowship with God and dependence on God, accepting that what God has for them is the best and that it is all they need.
But God is the Lord of life and death. The Transfiguration episode, in which Jesus is revealed in his heavenly glory on top of a mountain and Moses and Elijah come to speak to him, shows that when it suits God’s purposes, and when it is the best thing for humanity, God has the power and the right to send people who have already gone to live in his presence back to earth to fulfill a particular mission. (We don’t know how or in exactly what manner these two returned to earth; the Bible does not explain that.)
Luke says specifically that when Moses and Elijah appeared, they spoke with Jesus “about his departure, which he was about to bring to fulfillment at Jerusalem.” This means that they came to speak with him about how he would soon die as the Savior of the world. This was so important that God wanted to make sure that Jesus was prepared and informed beforehand, so God sent these two trusted servants of his to speak with Jesus about it.
That, by itself, is enough to show that this was not a violation of the command not to consult the dead, as people would do if they were trying to take matters into their own hands. Rather, God himself, the Lord of life and death, who gave that command to keep people in their proper sphere, exercised the authority of his own sphere and sent servants from the heavenly part of his realm to support and encourage a very special Servant who was then living in the earthly part of his realm.
But there is more. When Luke says “departure,” he uses the Greek term exodus. This is a hint that the appearance of Moses and Elijah also has symbolic significance. Moses, who let the Israelites out of Egypt in the Exodus, also wrote the first part of the Old Testament. Elijah represents the prophets, who composed or collected the next major part of the Old Testament. Later in the gospel of Luke, Jesus tells a parable in which Abraham tells someone who is concerned about his family members, “They have Moses and the Prophets; let them listen to them.” He doesn’t mean listen to them literally; he means to read their writings in the Scriptures. (By “Moses and the Prophets,” he means all the Scriptures that had been written by that time.)
And significantly, in the Transfiguration episode, God says, “This is my beloved Son. Listen to him.” So it seems that by sending Moses and Elijah, God was also signaling that Jesus would be the fulfillment of the Scriptures, certainly in his sacrificial death for the world, but also in his life and teaching. (People are to “listen to him” as they would “listen to” Moses and the Prophets, that is, the Scriptures.)
So there was both a practical reason and a symbolic significance for the special mission that God sent Moses and Elijah to accomplish. The fact that they did this by traveling temporarily from one part of God’s realm to another, on God’s instructions, does not mean that they violated God’s command for human beings to remain within their own realm and not try to call on other powers to get what they want. I hope this helps answer your question.
Good Question 
Mathew 17 : 9 And as they came down from the mountain, Jesus charged them, saying, Tell the vision to no man, until the Son of man be risen again from the dead.
COULD THE ANSWER NOT BE ……. IT WAS A ……. “”” VISION””””
Here the Greek expression τὸ ὅραμα, which many Bibles translate as “the vision,” can well be translated as “what you have seen,” as many other Bibles translate it. So, for example, the NIV and NLT, “Don’t tell anyone what you have seen, until the Son of Man has been raised from the dead.”