“All forms of divination are to be rejected: recourse to Satan or demons, conjuring up the dead or other practices falsely supposed to “unveil” the future. Consulting horoscopes, astrology, palm reading, interpretation of omens and lots, the phenomena of clairvoyance, and recourse to mediums all conceal a desire for power over time, history, and, in the last analysis, other human beings, as well as a wish to conciliate hidden powers. They contradict the honor, respect, and loving fear that we owe to God alone” (CCC 2116).
Consulting with mediums is also condemned in Deuteronomy 18:10-12:
“Let there not be found among you anyone who immolates his son or daughter in the fire, nor a fortune-teller, soothsayer, charmer, diviner, or caster of spells, nor one who consults ghosts and spirits or seeks oracles from the dead. Anyone who does such things is an abomination to the Lord, and because of such abominations the Lord, your God, is driving these nations out of your way.”
While mediums are often frauds, the Church in her wisdom, knows that such spiritistic phenomena can be used as a deceptive tool of the evil one to draw people to diabolical influences, which is why she “…opposes any participation whatsoever in spiritistic performances on account of their superstitious character and the dangers to which the faithful may be exposed as regards faith and morals.
In the Bible and in Christian hagiography we come across cases of deceased persons, of angels, and of demons appearing to the living to warn, help, tempt, or punish them. Such communications, however, always take place in a sober atmosphere, in which rules the will of God who arranges or permits them. In spiritism, on the contrary, we find a spectacle of exhibitionism, often grotesque, which is repugnant to the sanctity of God and to the dignity of the angels and the disincarnate spirits." (Dictionary of Dogmatic Theology by Msgr. Pietro Parente pg. 266).
At the moment of death, man’s soul is judged in a particular judgment: either entrance into the blessedness of heaven-through purification or immediately, --or immediate and everlasting damnation (CCC 1022).