In D&C 129 Joseph Smith gives us three grand keys whereby we can know whether any ministration is from God.
D&C 129:4 When a messenger comes saying he has a message from God, offer him your hand and request him to shake hands with you.
5 If he be an angel he will do so, and you will feel his hand.
6 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 –
7 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.
8 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.
9 These are three grand keys whereby you may know whether any administration is from God.
This counsel is only realized in part in this scripture. Those who are endowed have a more complete rendering of this counsel.
Why does Joseph Smith refer to this instruction as three grand keys? Keys unlock things. What does this unlock?
To understand what these keys unlock, we need to recognize what Joseph Smith observed “If the Church knew all the commandments, one-half they would condemn through prejudice and ignorance.” Ministers from the celestial realm are not sent to teach man that which he already knows.
Here is the point of the whole matter. If we ever find ourselves learning from such a messenger, his message will run very counter to our traditions and expectations. So much so, that we would never accept his message if we didn’t have a key, that would prove to ourselves that we were indeed hearing a messenger sent from Heaven, rather than a deception of the adversary.
That is why it is called a key, and that is what it unlocks.
Joseph Smith said “I have tried for a number of years to get the minds of the Saints prepared to receive the things of God; but we frequently see some of them, after suffering all they have for the work of God, will fly to pieces like glass as soon as anything comes that is contrary to their traditions: they cannot stand the fire at all. How many will be able to abide a celestial law, and go through and receive their exaltation, I am unable to say, as many are called, but few are chosen.” (TPJS 331)
We hear of angels (cherubim) that stand to guard the way of the tree of life. We learn that we need to pass angels and Gods that are set to guard the way to exaltation.
But we need a key to pass them. What does that mean?
It means that we cannot come up to their standard of living without having a way to verify that they are genuine, because without that, the things portrayed by them will be so foreign and unexpected to us that we will reject it, and thereby cut ourselves off, being unable to move forward past the point they were sent to lead us around.
Without a key, we cannot get past them.