Knowledge is a key of salvation
"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, as evil spirits will have more knowledge, and consequently more power than many men who are on the earth. Hence it needs revelation to assist us, and give us knowledge of the things of God." (Joseph Smith, HC 4:34)
We must search the mysteries
"I advise all to go on to perfection, and search deeper and deeper into the mysteries of Godliness." (Joseph Smith, HC 6:17)
We must seek to know the mysteries in full, otherwise we will be damned to hell
"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." (Alma, Alma 12:10-11)
"Contend earnestly for the like precious faith with the Apostle Peter, 'and add to your faith virtue,' knowledge, temperance, patience, godliness, brotherly kindness, charity; 'for if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.' Another point, after having all these qualifications, he lays this injunction upon the people 'to make your calling and election sure.' He is emphatic upon this subject—after adding all this virtue, knowledge, &c., 'Make your calling and election sure.' What is the secret—the starting point? 'According as His divine power hath given unto us all things that pertain unto life and godliness.' How did he obtain all things? Through the knowledge of Him who hath called him. There could not anything be given, pertaining to life and godliness, without knowledge....
"We have no claim in our eternal compact, in relation to eternal things, unless our actions and contracts and all things tend to this end. But after all this, you have got to make your calling and election sure. If this injunction would lie largely on those to whom it was spoken, how much more those of the present generation!
"1st key: Knowledge is the power of salvation. 2nd key: Make your calling and election sure. 3rd key: It is one thing to be on the mount and hear the excellent voice, &c., &c., and another to hear the voice declare to you, You have a part and lot in that kingdom." (Joseph Smith, HC 5:21)
"He then read the 7th chap. Hebrews....I say to all those who are disposed to set up stakes for the Almighty, You will come short of the glory of God.
"To become a joint heir of the heirship of the Son, one must put away all his false traditions.
"I prophesy and bear record this morning that all the combined powers of earth and hell shall not and cannot ever overthrow or overcome this boy, for I have a promise from the eternal God....
"The power of the Melchizedek priesthood is to have the power of "endless lives;" for the everlasting covenant cannot be broken....There are three grand orders of priesthood referred to here.
"1st. The King of Shiloam. (Salem) had power and authority over that of Abraham, holding the key and the power of endless life. Angels desire to look into it, but they have set up too many stakes. God cursed the children of Israel because they would not receive the last law from Moses.
"The sacrifice required of Abraham in the offering up of Isaac, shows that if a man would attain to the keys of the kingdom of an endless life; he must sacrifice all things. When God offers a blessing or knowledge to a man, and he refuses to receive it, he will be damned. The Israelites prayed that God would speak to Moses and not to them; in consequence of which he cursed them with a carnal law.
"What was the power of Melchizedek? 'Twas not the Priesthood of Aaron which administers in outward ordinances, and the offering of sacrifices. Those holding the fullness of the Melchizedek Priesthood are kings and priests of the Most High God, holding the keys of power and blessings. In fact, that priesthood is a perfect law of theocracy, and stands as God to give laws to the people, administering endless lives to the sons and daughters of Adam.
"Abraham says to Melchizedek, I believe all that thou hast taught me concerning the priesthood and the coming of the Son of Man; so Melchizedek ordained Abraham and sent him away. Abraham rejoiced, saying, Now I have a priesthood.
"Salvation could not come to the world without the mediation of Jesus Christ.
"How shall God come to the rescue of this generation? He will send Elijah the prophet. The law revealed to Moses in Horeb never was revealed to the children of Israel as a nation.
"Elijah shall reveal the covenants to seal the hearts of the fathers to the children, and the children to the fathers.
"The anointing and sealing is to be called, elected and made sure.
"Without father, without mother, without descent, having neither beginning of days nor end of 'life, but made like unto the Son of God, abideth a priest continually.' The Melchizedek Priesthood holds the right from the eternal God, and not by descent from father and mother; and that priesthood is as eternal as God Himself, having neither beginning of days nor end of life.
"The 2nd Priesthood is Patriarchal authority. Go to and finish the temple, and God will fill it with power, and you will then receive more knowledge concerning this priesthood.
"The 3rd is what is called the Levitical Priesthood, consisting of priests to administer in outward ordinance, made without an oath; but the Priesthood of Melchizedek is by an oath and covenant.
"The Holy Ghost is God's messenger to administer in all those priesthoods.
"Jesus Christ is the heir of this Kingdom—the only begotten of the Father according to the flesh, and holds the keys over all this world.
"Men have to suffer that they may come upon Mount Zion and be exalted above the heavens.
"I know a man that has been caught up to the third heavens, and can say, with Paul, that we have seen and heard things that are not lawful to utter." (Joseph Smith, HC 5:28)
Seer stone referred to as a key. All should have one.
"A short time before the house was completed, a man by the name of Josiah Stoal, came from Chenango County, New York, with the view of getting Joseph to assist him in digging for a silver mine. He came for Joseph on account of having heard that he possessed certain keys, by which he could discern things invisible to the natural eye." (Lucy Mack Smith, Biographical Sketches, 1853)
Keys as knowledge in detecting spirits:
"There are two kinds of beings in heaven, namely: Angels, who are resurrected personages, having bodies of flesh and bones—For instance, Jesus said: Handle me and see, for a spirit hath not flesh and bones, as ye see me have. Secondly: the spirits of just men made perfect, they who are not resurrected, but inherit the same glory. When a messenger comes saying he has a message from God, offer him your hand and request him to shake hands with you. If he be an angel he will do so, and you will feel his hand. If he be the spirit of a just man made perfect he will come in his glory; for that is the only way he can appear—Ask him to shake hands with you, but he will not move, because it is contrary to the order of heaven for a just man to deceive; but he will still deliver his message. If it be the devil as an angel of light, when you ask him to shake hands he will offer you his hand, and you will not feel anything; you may therefore detect him. These are three grand keys whereby you may know whether any administration is from God." (D&C Section 129, 1843)
Keys to know how to detect Satan
"Brother Joseph taught many and important principles to benefit and bless them their mission teaching them to observe charity wisdom and a fellow feeling for each other and love one another in all things and under all circumstances unfolding keys of knowledge to detect Satan and preserve in the favor of God." (Heber C. Kimball, July 2, 1839)
"Among the vast number of the Keys of the Kingdom of God Joseph presented the following one to the Twelve for there benefit in there experience & travels in the flesh which is as follows. In order to detect the devel when he transforms himself nigh unto an angel of light..." (Wilford Woodruff, Journal. June 27, 1839)
Keys are knowledge of signs, must "know them all"
"I preached in the grove, on the keys of the kingdom, charity, &c. The keys are certain signs and words by which false spirits and personages may be detected from true, which cannot be revealed to the Elders till the Temple is completed. The rich can only get them in the Temple, the poor may get them on the mountain top as did Moses. The rich cannot be saved without charity, giving to feed the poor when and how God requires, as well as building. There are signs in heaven, earth and hell; the Elders must know them all, to be endowed with power, to finish their work and prevent imposition. The devil knows many signs, but does not know the sign of the Son of Man, or Jesus. No one can truly say he knows God until he has handled something and this can only be in the holiest of holies." (Joseph Smith, HC 4:35, May 1, 1842)
Keys as instructions
"They were so sacred that when Heber C. Kimball wrote to fellow apostle Parley P. Pratt just a few weeks later, he said that Joseph had taught them some precious things on the priesthood that would cause his soul to rejoice if he knew them, but that Joseph had given instructions that these keys not be written about. Heber concluded his description of the newly revealed endowment by saying that Parley would have to come to Nauvoo to receive the instruction for himself." (Letter of Heber C. Kimball to Parley P. Pratt, 17 June 1842, Church Archives, The Words of Joseph Smith)
"John wrested the keys, the kingdom, the power, the glory from the Jews, by the holy anointing and decree of heaven..." (Joseph Smith, TPJS)
"[John] was baptized while he was yet in his childhood, and was ordained by the angel of God at the time he was eight days old unto this power, to overthrow the kingdom of the Jews, and to make straight the way of the Lord before the face of his people, to prepare them for the coming of the Lord, in whose hand is given all power." (D&C 84:28)
It can be said that John was raised up, in part, as an authorized messenger to be rejected by the Jews, so he could wrest the keys from them.