In Joseph Smith's vision of the three degrees of glory found in D&C Section 76 he talks about the celestial, the terrestrial and telestial glories, giving a description of those who will go there and what blessings they will have. While this section is largely our only source in scripture for understanding the three degrees of glory, D&C Section 131 also has a brief statement about the "celestial glory". All it includes is four verses stating:
1 In the celestial glory there are three heavens or degrees;It is from this first verse that we get the idea that the celestial glory is further divided into three more levels or degrees. The first revelation (section 76) was received in 1832 and the second one was received in 1843, thus it is assumed that the second revelation (section 131) was received as a small addendum to the doctrine given in 1832. In other words, the fact that there were three levels within the celestial kingdom was something that was missed by Joseph Smith in the original vision that was added on later (in about 1843) to flesh-out our understanding of the celestial kingdom. At least that was the conventional wisdom being taught in seminary.
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];
3 And if he does not, he cannot obtain it.
4 He may enter into the other, but that is the end of his kingdom; he cannot have an increase.
Today there is a common phrase in the church about "the highest level of the celestial kingdom". This phrase is common enough that most members can at least repeat it and say something about it, mainly they heard it from so-and-so that ______(fill in the blank, with appropriate reference to general authority, prophet, book, scripture, rumor, myth, mormon musical etc.).
My thought is that in the original vision seen by Joseph Smith he never mentioned anything remotely alluding to separate levels within the celestial kingdom. As a matter of fact there is language contained in section 76 that would imply that there is no sub-dividing levels within the celestial kingdom. For example verses 92-96 state:
92 And thus we saw the glory of the celestial, which excels in all things—where God, even the Father, reigns upon his throne forever and ever;As we read in verse 95, those who partake of celestial glory are "equal in power, and in might, and in dominion". It seems to me that that would preclude there being any levels or distinctions between people in the celestial kingdom. If we look at what is said about the other kingdoms the only place we find subdivisions or distinctions within the kingdom is in the telestial kingdom where, "as one star differs from another star in glory, even so differs one from another in glory in the telestial world" (v. 98). This difference is distinctly absent from the other kingdoms. So if it is the case that the people in the celestial kingdom are "equal in power, and in might, and in dominion" then it would be illogical for there to be three levels or degrees within the celestial kingdom.
93 Before whose throne all things bow in humble reverence, and give him glory forever and ever.
94 They who dwell in his presence are the church of the Firstborn; and they see as they are seen, and know as they are known, having received of his fulness and of his grace;
95 And he makes them equal in power, and in might, and in dominion.
96 And the glory of the celestial is one, even as the glory of the sun is one.
But if we return to section 131 we have the statement in the first verse which clearly states that "In the celestial glory there are three heavens or degrees". This would seem to be a contradiction from the complete lack of levels within the celestial kingdom from section 76. But if we think about it we should consider the phrase "celestial glory" and how it is being used, or specifically how Joseph Smith used it. In our modern times members of the church would be picky about the use of the word celestial to only mean those things pertaining to the celestial kingdom (i.e. the highest kingdom as explained in section 76). I do not think that at the time Joseph Smith was as particular with his words as we are today. That is, he was not working with the definition that we have built up around the word "celestial". It is most likely that when he used the phrase "celestial glory" in the context of section 131 he simply meant anything that was part of our post-mortal experience.
Thus the three degrees referred to in section 131 are not referring to three previously undisclosed levels of glory within the glory of the celestial kingdom, but in fact refer to the three known kingdoms of glory, what we call the celestial, the terrestrial and the telestial. If we consider it like this then we have less contradictions to explain in the scriptures. As a final parting note, there is even a short Wikipedia stub about the separation degrees within the celestial kingdom. As the source they cite section 131 and then reference section 132 verses 16 and 17 to explain the two unexplained levels within the celestial kingdom. But if we take a look at these two verses we read:
16 Therefore, when they are out of the world they neither marry nor are given in marriage; but are appointed angels in heaven, which angels are ministering servants, to minister for those who are worthy of a far more, and an exceeding, and an eternal weight of glory.These verses are used as support for the subdivisions inside the celestial kingdom in order to explain what happens to the people in the other two levels, i.e. those not exalted to the highest level. They are made "ministering servants" to those who are exalted to "the highest level", but they are still part of the celestial kingdom, according to this interpretation. The problem with this is that in verse 17 it specifically states that these "ministering servants" "are not gods", which again goes directly contrary to what we find in section 76 which states (verse 58), "Wherefore, as it is written, they are gods, even the sons of God" referring to those who receive celestial glory. Thus we have another contradiction between sections 132 and 76, but only if we assume that the "ministering servants" referred to in 132 are part of the celestial kingdom and make up the two lower levels of the celestial kingdom. But if we take the idea that there are no levels within the celestial kingdom and that the only distinctions come from the three main degrees of glory then we no longer have this contradiction and the "ministering servants" are clearly members of a different or lower kingdom and do not partake of the fullness given to those of celestial glory.
17 For these angels did not abide my law; therefore, they cannot be enlarged, but remain separately and singly, without exaltation, in their saved condition, to all eternity; and from henceforth are not gods, but are angels of God forever and ever.
Of course all this hinges on the fact that Joseph Smith may not have been using the phrase "celestial glory" in the same way that we are accustomed to use it now, which I think is much more likely than the contradictions that arise from assuming that there are multiple levels within the celestial kingdom, where all are "equal in power, and in might, and in dominion" and all are "gods, even the sons of God".