JOEL - This is refering to the Law of Adoption; a principle that was practiced among the early saints whose other family members were not church members. They believed that if they were sealed or "adopted" to Joseph Smith or other church leaders it would assure themslves of exaltation in the next life. So many men and women were sealed to Joseph Smith(or to some of the Apostles) both before and after his death.
According to Wilford Woodruff:
"I say let every man be adopted to his father; and then you will do exactly what God said when he declared He would send Elijah the prophet in the last days. . . . We want the Latter-day Saints from this time to trace their genealogies as far as they can, and to be sealed to their fathers and mothers. Have children sealed to their parents, and run their chain through as far as you can get it. When you get to the end, let the last man be adopted to Joseph Smith, who stands at the head of this dispensation. This is the will of the Lord to this people, and I think when you come to reflect upon it you will find it to be true."
(Woodruff's sermon was published in several places. Text quoted taken from The Deseret Weekly 48 (1894) 541-44. See also The Deseret Evening News, 14 April 1894.
See also "The Law of Adoption: One Phase of the Development of the Mormon Concept of Salvation", 1830-1900 by Gordon Irving 1, BYU Studies, vol. 14 (1973-1974))
The saints began to misuse this practice however so God directed President Woodruff to discontinue the spiritual adoptions and thereafter sealings were performed only with blood relatives, omitting the part about being adopted to Joseph Smith(or other Apostles). Wilford Woodruff explained why it should be discontinued:
"I have prayed over this matter, and my brethren have. We have felt, as President Taylor said, that we have got to have more revelation concerning sealing under the law of adoption. Well, what are these changes? One of them is the principle of adoption. In the commencement of adopting men and women in the temple at Nauvoo, a great many persons were adopted to different men who were not of the lineage of their fathers, and there was a spirit manifested by some in that work that was not of God. Men would go out and electioneer and labor with all their power to get men adopted to them. One instance I will name here: A man went around Nauvoo asking every man he could, saying, "You come and be adopted to me, and I shall stand at the head of the kingdom, and you will be there with me." Now, what is the truth about this? Those who were adopted to that man, if they go with him, will have to go where he is. He was a [participant] in that horrible scene-the Mountain Meadow massacre. . . . When I went before the Lord to know who I should be adopted to (we were then being adopted to prophets and apostles), the Spirit of God said to me, "Have you not a father, who begot you?" "Yes, I have." "Then why not honor him? Why not be adopted to him?" "Yes," said I, "that is right." I was adopted to my father, and should have had my father sealed to his father, and so on back; and the duty that I want every man who presides over a temple to see performed from this day henceforth and forever, unless the Lord Almighty commands otherwise, is, let every man be adopted to his father. When a man receives the endowments, adopt him
to his father; not to Wilford Woodruff, nor to any other man outside the lineage of his fathers. That is the will of God to this people... (May 28, 1894)
(The Discourses of Wilford Woodruff, Bookcraft, Salt Lake City, Utah 1946, 154-157)
If you have the new "Teachings of the Presidents of the Church: Wilford Woodruff", you can read more about this on page xxxiv.