http://muhlestein.info/journalofdiscourses/Vol_02/index.htm
Some excerpts are provided below:
[Pratt begins his discourse by citing Isaiah on “familiar spirits”]:
“And when they shall say unto you, seek unto them that have familiar spirits, and unto wizards that peep and mutter; should not a people seek unto their God? for the living to hear from the dead?”
[Pratt relates the Isaiah text to the Book of Mormon]:
“The foregoing text was copied by Nephi, from the Book of Isaiah, about six hundred years before Christ, and is now contained in the second Book of Nephi, chap. ix.”
[Pratt then describes how the world has come to accept the possibility of communication with the dead]:
“For the last few years the world has been disturbed very much by alleged communications from the world of spirits. “Mesmerism,” “Clairvoyance,” “Spiritual Knockings,” “Writing Mediums,” &c., are said to be channels of communication between the living and the dead. How often one meets with an invitation to seek to some “medium”-to some one “familiar with spirits,” in order to hear from a deceased father, mother, husband, wife, or other relative or friend.”
[Pratt points out that some oppose the idea that the dead can communicate with the living]:
“On the other hand, these alleged communications from the spirit world are zealously opposed, on the ground that there is no such philosophy in nature; that there can be no medium of communication between the living and those who have passed the vale of death; and that, therefore, all alleged communications from that source must necessarily be false.”
[Pratt says that the faithful cannot deny that the dead communicate with the living or they will be denying the very foundation of the Church]:
“….If, on the other hand, we deny the philosophy or the fact of spiritual communication between the living and those who have died, we deny the very fountain from which emanated the great truths or principles which were the foundation of both the ancient and modern Church.”
[Pratt gives scriptural examples of the dead communicating with the living then says]:
“Shall we, then, deny the principle, the philosophy, the fact of communication between worlds? No! verily no!”
[Pratt then rejoices that the rest of the world now recognizes the importance of spirit world communication]:
“Editors, statesmen, philosophers, priests, and lawyers, as well as the common people, began to advocate the principle of converse with the dead, by visions, divination, clairvoyance, knocking, and writing mediums, &c., &c. This spiritual philosophy of converse with the dead, once established by the labors, toils, sufferings, and martyrdom of its modern founders, and now embraced by a large portion of the learned world, shows a triumph more rapid and complete-a victory more extensive, than has ever been achieved in the same length of time in our world.”
[Pratt continues, now emphasizing that other groups that communicate with the dead use “unlawful mediums” or improper “channels of communication”]:
“The fact of spiritual communications being established, by which the living hear from the dead-being no longer a question of controversy with the well informed, we drop that point, and call attention to the means of discriminating or judging between the lawful and the unlawful mediums or channels of communication-between the holy and impure, the truths and falsehoods, thus communicated.”
[Pratt concludes that only those who hold the keys of the Priesthood can properly communicate with the dead]:
“It is, then, a matter of certainty, according to the things revealed to the ancient Prophets, and renewed unto us, that all the animal magnetic phenomena, all the trances and visions of clairvoyant states, all the phenomena of spiritual knockings, writing mediums, &c., are from impure, unlawful, and unholy sources; and that those holy and chosen vessels which hold the keys of Priesthood in this world, in the spirit world, or in the world of resurrected beings, stand as far aloof from all these improper channels, or unholy mediums, of spiritual communication, as the heavens are higher than the earth, or as the mysteries of the third heaven, which are unlawful to utter, differ from the jargon of sectarian ignorance and folly, or the divinations of foul spirits, abandoned wizards, magic-mongers, jugglers, and fortune-tellers.”