Joseph Smith taught that it is critical for us to know the mysteries of God. "Knowledge saves a man; and in the world of spirits no man can be exalted but by knowledge." TPJS, p. 357.
"A man is saved no faster than he gets knowledge, for if he does not get knowledge, he will be brought into captivity by some evil power in the other world." TPJS, p. 217.
Joseph understood we are saved by gaining knowledge about God’s mysteries. When we are ignorant of them, we cannot be saved. No one can be saved in ignorance. It is not possible.
Joseph's knowledge mirrored what is taught and reflected in the Book of Mormon:
Alma 12: 9-11 explains:
“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. 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. And they that will harden their hearts, to them is given the lesser portion of the word until they know nothing concerning his mysteries; and then they are taken captive by the devil, and led by his will down to destruction. Now this is what is meant by the chains of hell.”
The definition of being taken captive by the devil is to “know nothing concerning [God’s] mysteries.”
When a person knows nothing concerning God’s mysteries, they are then “led by his [the devil’s] will down to destruction.”
When they are taken captive by their ignorance, they are then bound “by the chains of hell.”
The result of ignorance of God’s mysteries is “destruction” and “captivity.” The ignorant will remain devoted to falsehoods, blinded leaders, and guides who give no truthful accounts of the awful situation faced by the ignorant because they do not understand truth.
D&C 93: 24-25: “And truth is knowledge of things as they are, and as they were, and as they are to come; And whatsoever is more or less than this is the spirit of that wicked one who was a liar from the beginning.”
We must know the truth. The truth informs us how things are (now, today, in the peril we presently face–unvarnished and in all its terrible meaning).
The truth informs us of how things were (by accurate history, revealing exactly what happened, without mythical or political overlay, with its disappointments and tragedies candidly depicted).
The truth informs us of the things to come (even if the prophecies and promises dash our hopes, crush our vanity and expose our foolishness).
Truth can be startling, but it is necessary. Without the truth it is impossible to repent. We will never change while trusting a lie. But we will never fail to repent when the truth is laid bare before us.
In order to take people captive, all that is required is for people to be content with their ignorance. The greatest threat to salvation does not come from teaching false doctrine, but instead comes from ignoring doctrine altogether. Substituting platitudes and truisms for careful, ponderous and solemn investigation of the deep things of God will suffice to keep people in the chains of captivity. It isn't necessary for the devil to convince you of lies, only for him to make you content in your ignorance, or fearful of the search for truth.