Baptism For The Dead Was Revealed A Little At A Time

The Prophet Brigham Young taught this about baptism for the dead,

Do you recollect that in about the year 1840-41, Joseph had a revelation concerning the dead? He had been asked the question a good many times: "What is the condition of the dead, those that lived and died without the Gospel?" It was a matter of inquiry with him. He considered this question for himself, and for the brethren and the Church, "What is the condition of the dead? What will be their fate? Is there no way today by which they can receive their blessings as there was in the days of the Apostles, and when the Gospel was preached upon the earth in ancient days?" When Joseph received the revelation that we have in our possession concerning the dead, the subject was opened to him, not in full, but in part, and he kept on receiving. When he had first received the knowledge by the spirit of revelation how the dead could be officiated for, there are brethren and sisters here, I can see quite a number here who were in Nauvoo, and you recollect that when this doctrine was first revealed, and in hurrying in the administration of baptism for the dead, that sisters were baptized for their male friends, were baptized for their fathers, their grandfathers, their mothers and their grandmothers, etc. I just mention this so that you will come to understanding, that as we knew nothing about this matter at first, the old Saints recollect, there was little by little given, and the subject was made plain, but little was given at once. Consequently, in the first place people were baptized for their friends and no record was kept. Joseph afterwards kept a record. Then women were baptized for men and men for women, etc. It would be very strange, you know, to the eyes of the wise and those that understood the things pertaining to eternity, if we were called upon to commence a work that we could not finish.     
This, therefore, was regulated and all set in order; for it was revealed that if a woman was baptized for a man, she could not be ordained for him, neither could she be made an Apostle or a Patriarch for the man, consequently the sisters are to be baptized for their own sex only.     
This doctrine of baptism for the dead is a great doctrine, one of the most glorious doctrines that was revealed to the human family; and there are light, power, glory, honor and immortality in it. 16:165.     
            (Brigham Young, Discourses of Brigham Young, selected and arranged by John A. Widtsoe, p.398-399)