Praying for the dead — Pagan practice.
I must admit, that I have not attended a single funeral, either Protestant or Catholic, where the minister/priest did not pray for the repose of the deceased’s soul with God, and ask the assembled mourners to join in that prayer.
I, a Protestant, pray for the souls of those I know whose bodies have died to go to heaven and be joined with our Savior and His Father there.
.
I guess those folks will NOT be part of the "dead in Christ".
1 Thessalonians 4:16
For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:
As long as you understand that the prayer is more for you and your peace of mind, and has no effect on their eternal destination. That fate is sealed once they pass from this life. If they are saved, Heaven is their destination. If they are lost, your prayers after the fact will not change this.
Just because it has become a practice of many to pray for the souls of the deceased, we should not then fall prey to the heretical idea that a soul's fate can be changed once they die. "It is appointed unto men once to die; after this, the judgment."