Glory comes proportional to the degree of the law lived. Those who limit themselves to the law they currently understand cannot advance to higher states of glory:
21 And they who are not sanctified through the law which I have given unto you, even the law of Christ, must inherit another kingdom, even that of a terrestrial kingdom, or that of a telestial kingdom.
22 For he who is not able to abide the law of a celestial kingdom cannot abide a celestial glory.
23 And he who cannot abide the law of a terrestrial kingdom cannot abide a terrestrial glory.
24 And he who cannot abide the law of a telestial kingdom cannot abide a telestial glory; therefore he is not meet for a kingdom of glory. Therefore he must abide a kingdom which is not a kingdom of glory. (D&C 88)
While spiritual stagnation is comfortable, it is also damning. It is easy and comfortable to live your religion when you assume that it will always be the same: your spiritual practices will never change, nor will the requirements of salvation. However, every saved person in the scriptures— every person with whom God made a covenant—was constantly subjected to principles that were beyond their previous comprehension despite their righteous lives. Abraham was asked to sacrifice Isaac, Moses was astounded by things he had never before supposed, etc. This is because we are not like God. We possess the degree of glory associated with the degree of the law we live. If we live a Celestial law, we possess Celestial glory, Terrestrial law, Terrestrial glory, and so on (see D&C 88:20-35). In order to ascend to a higher degree of glory, we will always need to embrace a set of laws of which we are ignorant. If you live your current beliefs perfectly, and have not been brought back into God’s presence, your current beliefs do not possess the power to bring you back into God’s presence. Like it or not, this means you necessarily do not possess the same beliefs as Jesus and all people who, by learning from him, obtained salvation. Therefore, coming up to a Celestial glory will require letting go of at least some of the things you currently hold as true. You cannot close yourself to ideas you perceive as contradictory to current beliefs and simultaneously let in further light and truth.
Not even Jesus himself possessed all there was to know in the beginning:
13 And he received not of the fulness at first, but continued from grace to grace, until he received a fulness;
14 And thus he was called the Son of God, because he received not of the fulness at the first. (D&C 93)
Those who believe that they already know all the doctrines necessary to be saved presume they know more than Jesus did, as he had to progress from one teaching to the next. They presume that, while Enoch and his city required hundreds of years to become Zion, they can do it with what little they learn at church! Enoch learned new fundamental truths about God’s character after having been in heaven with God for generations. As the Lord said:
8 For my thoughts are not your thoughts, neither are your ways my ways, saith the Lord.
9 For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts. (Isaiah 55)
Frankly, no one knows everything there is to know. If Jesus, Enoch, and others still had a lot to learn, we should be very cautious in our assertions of what we “know” to be true. Otherwise, we fall into the category of those who think they are wise, which incidentally means precisely that we do not hearken to God:
O that cunning plan of the evil one! O the vainness, and the frailties, and the foolishness of men! When they are learned they think they are wise, and they hearken not unto the counsel of God, for they set it aside, supposing that they know of themselves, wherefore, their wisdom is foolishness and it profiteth them not. And they shall perish. (2 Nephi 9:28)
Never think that what you have is enough, or the end, or final. “Wo be unto him that shall say: We have received the word of God, and we need no more of the word of God, for we have enough!” (2 Nephi 28:29) There is no such thing as final truth. Alma taught:
9 ...It is given unto many to know the mysteries of God; nevertheless they are laid under a strict command that they shall not impart only according to the portion of his word which he doth grant unto the children of men, according to the heed and diligence which they give unto him.
10 And therefore, he that will harden his heart, the same receiveth the lesser portion of the word; and he that will not harden his heart, to him is given the greater portion of the word, until it is given unto him to know the mysteries of God until he know them in full. (Alma 12)
No matter how sure you are about anything, no matter the criticality of your understanding of a certain doctrine to your entire belief structure, always consider the possibility that you are wrong. The only way to know, of course, is to ask the Lord.
Joshua and the Elders of Israel failed to do so when approached by emissaries from one of the nations the Lord had commanded to be destroyed. Falling for the disguise and false story, the Israelites made an oath with the emissaries, who claimed to be from a far distant land, to allow them to be their servants. Unfortunately, “the men...asked not counsel at the mouth of the Lord.” (Joshua 9:14) The Israelites foolishly made an oath to protect the men and their nation, and thus could not comply with the Lord’s command to destroy them. At least some of the idolatry and eventual apostasy of Israel can be traced to this one incident of overconfidence in the understanding of men.
Damnation is literally to advance no further. Those who refuse new truths from God (they cannot come from any other source—though they may come through many sources, including people we presume to be fools) will be permanently limited in their eternal progression, because higher law is required for higher blessings. “All kingdoms have a law given; And there are many kingdoms...And unto every kingdom is given a law; and unto every law there are certain bounds also and conditions. All beings who abide not in those conditions are not justified.” (D&C 88:36, 38-39) When God offers a blessing or knowledge to someone, and they refuse it, they are damned—it will permanently block them from obtaining what otherwise could have been theirs:
For behold, thus saith the Lord God: I will give unto the children of men line upon line, precept upon precept, here a little and there a little; and blessed are those who hearken unto my precepts, and lend an ear unto my counsel, for they shall learn wisdom; for unto him that receiveth I will give more; and from them that shall say, We have enough, from them shall be taken away even that which they have. (2 Nephi 28:30)
It may seem difficult to imagine that thinking you know something and failing to hearken to God are the same. Yet, Jacob equates it to being deaf (see 2 Nephi 9:31) and blind (see 2 Nephi 9:32), probably because God continues to reveal new things to everyone as long as they continue to listen to him. Therefore, if you become set in your idea of the truth, you could only have become so by ignoring what God is continuing to say to you. Living revelation means constant revelation. We should expect to frequently displace our current understanding with something better.
If one assumes that they lack knowledge, the next step is to seek it. If we want to learn more than we know, we will have to investigate points of view that don’t belong to us already. While it is possible that new knowledge exists outside the bounds of accepted truth, scriptural examples suggest it is much more likely that further light and truth will clash with what we already think we know than support it. However, this gives us no reason to fear reading or hearing information that doesn’t agree with what we believe. After all, if we believe man is fallen and God is perfect, we ought to understand that his revelation of our misconceptions is how we become more like him.
You should not assume something is false simply because you have never heard it before. Anyone who does not believe they know everything ought to expect to hear something that they’ve never heard before, or something that contradicts what they have been told previously.
Searching for truth requires a willingness to investigate both sides of a position as objectively as possible. If you are merely arguing for your position, you cannot honestly say you are searching for truth. You do not know all things, and therefore you cannot ever be totally sure that you are right. If you aren't willing to be wrong about something, you can only go so far in your search for truth.
Knowledge of opposing views is absolutely necessary for two reasons. First, a rational position requires knowledge of both sides of an issue. For example, how could you honestly say that one variety of apple is the tastiest if you’ve never tried another variety? Second, you cannot effectively persuade others if you are not aware of why they believe what they do.
Knowing your counterpart’s reasons for their belief is a two-fold benefit. First, construction of a persuasive argument on your part requires you to address their reasons for believing. How could you persuade a fan of Golden Delicious apple that Granny Smith is superior if you have never actually tried Golden Delicious? The strength of your position depends on your addressing their reasons for believing. Secondly, an intrinsic benefit of investigating your opponent’s position is the possible discovery that they are, in fact, correct. Just as you could possess evidences of your position that your counterpart had never considered, so could they. You could very well end up supporting their position should their evidence prove stronger than yours. Yet, such a situation is to be desired, not feared, for those in possession of greater truth have drawn closer to God.
For most, unbiased evaluation of opposing views is particularly difficult. After all, no one wants to turn away from their life's work, or the legacy of their ancestors. The more that is sacrificed for a belief system, the less likely one is to abandon that belief system. The loss isn't all ideological, either.
Accepting putative truth might cost you your job, your loved ones, or anything else your heart might be attached to. In order to maintain objectivity, one must adopt a posture where they can temporarily detach from their persona and consider putative truth absent of what it would cost them if it were true, what they think of the source, etc. The search for truth must be detached from our temporal and philosophical circumstance.