“Dead” as described in Deuteronomy does not necessarily refer to physical death, but to those who have left this Earthly, physical existence and crossed over into a spiritual existence.
Revelation 5:8
And when he had taken it, the four living creatures and the twenty-four elders fell down before the Lamb. Each one had a harp and they were holding golden bowls full of incense, which are the prayers of the saints.
Revelation 5:7-9 (in Context) Revelation 5 (Whole Chapter)
Revelation 8:3
Another angel, who had a golden censer, came and stood at the altar. He was given much incense to offer, with the prayers of all the saints, on the golden altar before the throne.
Revelation 8:2-4 (in Context) Revelation 8 (Whole Chapter)
Revelation 8:4
The smoke of the incense, together with the prayers of the saints, went up before God from the angel’s hand.
Revelation 8:3-5 (in Context) Revelation 8 (Whole Chapter)
catholic.com/library/Praying_to_the_Saints.asp
It does not make the distinction between “dead” and “dead in Christ”. All prayers to the dead are forbidden.
Sometimes Fundamentalists object to asking our fellow Christians in heaven to pray for us by declaring that God has forbidden contact with the dead in passages such as Deuteronomy 18:10–11.
In fact, he has not, because he at times has given it—for example, when he had Moses and Elijah appear with Christ to the disciples on the Mount of Transfiguration (Matt. 17:3). Moses and Elijah are not dead. But they are certainly in Heaven.
And if you do not have a problem with us speaking with living people then why don’t you pray with Moses and Elijah toward Jesus?
What God has forbidden is necromantic practice of conjuring up spirits. “There shall not be found among you any one who burns his son or his daughter as an offering, any one who practices divination, a soothsayer, or an augur, or a sorcerer, or a charmer, or a medium, or a wizard, or a necromancer. . . . For these nations, which you are about to dispossess, give heed to soothsayers and to diviners; but as for you, the Lord your God has not allowed you so to do. The Lord your God will raise up for you a prophet like me from among you, from your brethren—him you shall heed” (Deut. 18:10–15).
God thus indicates that one is not to conjure the dead for purposes of gaining information; one is to look to God’s prophets instead.
Thus one is not to hold a seance. But anyone with an ounce of common sense can discern the vast qualitative difference between holding a seance to have the dead speak through you and a son humbly saying at his mother’s grave, “Mom, please pray to Jesus for me; I’m having a real problem right now.”
The difference between the two is the difference between night and day. One is an occult practice bent on getting secret information; the other is a humble request for a loved one to pray to God on one’s behalf.