If you are talking about the incident with King Saul and the departed Samuel, that was before Christ defeated death.
Also, a very common exegesis, among Orthodox and Protestants, is that that was not actually the ghost of King Saul but a spirit impersonating him. This makes sense in light of the Witch of Endor being, lets be fair, a witch, who was violating the divine law concerning necromancy.
In fact the
Orthodox Study Bible has this to say about the Witch of Endor incident:
“This passage created great controversy among the Fathers of the Church. In fact, at least three distinct interpretations can be found.
1. The woman called Samuel forth from the dead (Justin Martyr, Origen, Ambrose, and Augustine).
2. Whether it was Samuel or a demon, it appeared at God's bidding and not by some magic of the woman (Chrysostom, Theodoret).
3. The entity was a demon who deceived Saul and gave him a false prophecy (Tertullian, Hippolytus, Ephrem the Syrian, Evagrius, Basil, Jerome, Ambrosiaster, & Gregory of Nyssa).
The third interpretation seems to be held by the greatest number of Fathers, and Gregory of Nyssa wrote a specific treatise on the subject. He defends this view by citing the impassible chasm in the Lazarus parable (Lk 16:26). The apparition appeared only to the woman; she told Saul whom it resembled. The Greek word translated medium in this passage is literally the word for “ventriloquist.” Also, Saul had been plagued by evil spirits for years and was easily deceived by them.”
Now, while I do not respect Theodoret, and Tertullian sadly fell into heresy, I have great respect for Origen and Augustine, and even more respect for Justin Martyr, Ambrose, and John Chrysostom, but I also hold in the same esteem the Cappadocians, Ephrem the Syrian, Jerome and Hippolytus, and their view seems to be, according to the St. Athanasius Academy which translated the Septuagint into English for the OSB and authored the commentary with representatives of all of the major Orthodox churches, the consensus patrum.
While (curiously) as far as I am aware Rome has not pronounced magisterially on the topic, Martin Luther, John Calvin, and King James I of England all regarded the apparition of Samuel as an apparition of diabolical or demonic origin, a rare moment of concord between the Lutheran, Reformed and High Church Anglican parties in the context of the later 16th century, and I know of no mainstream Protestant theologians who differ from their views and those of the Cappadocians and Sts. Ephrem, Jerome and Hippolytus.
Conversely the prevailing view in Rabinnical Judaism is that it was a real apparition of Samuel; Josephus believed this, other Jewish theologians speculated that in the first year following burial, the spirit of the deceased could wander, and the Haggadah on the subject further confirms the idea the Witch of Endor was real, and further speculates on the nature of mediums and their ability to communicate with the deceased. I do not know what Karaites, Samaritans, or Beta Israel think of it, but it would be interesting to find out.