Doctrine and Covenants of the Church of Jesus Christ of the Latter-Day Saints, at sacred-texts.com

131. Instructions given by Joseph Smith, Ramus, Illinois, May 16 and 17, 1843.
History of the Church 5:392-93.

131:1 In the celestial glory there are three heavens or degrees;

131:2 And in order to obtain the highest, a man must enter into this order of the priesthood [meaning the new and everlasting covenant of marriage];

131:3 And if he does not, he cannot obtain it.

131:4 He may enter into the other, but that is the end of his kingdom; he cannot have an increase.

131:5 (May 17th, 1843.) The more sure word of prophecy means a man's knowing that he is sealed up unto eternal life, by revelation and the spirit of prophecy, through the power of the Holy Priesthood.

131:6 It is impossible for a man to be saved in ignorance.

131:7 There is no such thing as immaterial matter. All spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes;

131:8 We cannot see it; but when our bodies are purified we shall see that it is all matter.