It’s in Deuteronomy - it is forbidden to attempt to talk with the deceased.
I found this - Elder Cleopa talking about Saul being punished by God for attempting to talk with ghosts:
“Those who concern themselves with this and call upon the spirits of the dead, bring in as support the example of Saul who sought from the sorceress the invocation of the soul of Samuel (1 Sam. 28). Those who have fallen into this delusion of Saul should know from his punishment that they are culpable before God. For, because of this very transgression, Saul lost his kingdom and his life and was punished by God to be killed with his own sword. The punishment of Saul for his unlawful conversing with the dead is related in Holy Scripture thus: So Saul died for his transgression which he committed against the LORD, even against the word of the LORD, which he kept not, and also for asking counsel of one that had a familiar spirit, to inquire of it; and inquired not of the LORD: therefore he slew him, and turned the kingdom unto David the son of Jesse (1 Chr. 10:13-14).
In the Old Testament the Lord commands the following: Regard not them that have familiar spirits, neither seek after wizards, to be defiled by them: I am the LORD your God (Lev. 19:31). And elsewhere: A man or also woman that hath a familiar spirit, or that is a wizard, shall surely be put to death: they shall stone them with stones: their blood shall be upon them (Lev. 20:27). The invocation of the spirits of the dead is hateful before God Who has never given it sanction among His people: … there shall not be found among you any one that maketh his son or his daughter to pass through the fire, or that useth divination, or an observer of times, or an enchanter, or a witch, or a charmer, or a consulter with familiar spirits, or a wizard, or a necromancer. For all that do these things are an abomination unto the LORD (Deut. 18:9-14). God considers this abomination one of man’s greatest revolts against His Will.”
http://orthodoxinfo.com/inquirers/ec_magic_occultism.aspx
Here is another thought in my head - how do you know who answers when they do answer? You kind of have to end up in trusting a voice or presence you can’t see, you know it is not God because you were not invoking God but someone who would just answer, while you are material and frail and capable of being objected by that presence easily.
But my greatest concern would be displeasing God, because it is Him who we must fear not a ghost. You go there thinking you are strong in faith and will be alright. But what if that ghost will scare you and all your fear will be dedicated to it? You will lose your confidence in your faith and bring unhappiness to you out of pure…curiosity (like Eve’s).