It is not uncommon for the Lord to reveal that which is unexpected in companion with that which is necessary and fundamental.
This forces us to choose between accepting the unexpected, or rejecting the necessary.
We see this in D&C 13.
D&C 13 Upon you my fellow servants, in the name of Messiah I confer the Priesthood of Aaron, which holds the keys of the ministering of angels, and of the gospel of repentance, and of baptism by immersion for the remission of sins; and this shall never be taken again from the earth, until the sons of Levi do offer again an offering unto the Lord in righteousness.
There you have it. The authority to do baptism. This is necessary and fundamental. We cannot reject this without rejecting that which is crucial.
Thus included with the Priesthood of Aaron came not only keys of the gospel of repentance, and of baptism by immersion for the remission of sins, but also the keys of the ministering of angels. That last one is unexpected. It would be more convenient if it was missing. Most of us don’t believe the ministering of angels plays an essential role in the gospel similar to the role of “repentance” or “baptism by immersion”. We tend to believe angels are a gospel perk reserved for prophets and apostles.
But we can’t reject the ministering of angels part without rejecting the whole revelation, and we can’t reject the whole revelation and still have baptism by God’s own authority.
One sees the same thing in D&C 84 and D&C 107. They offer great insight into the priesthood, but it includes much that is unexpected.
D&C 84:19 And this greater priesthood administereth the gospel and holdeth the keys of the mysteries of the kingdom, even the key of the knowledge of God.
20 Therefore, in the ordinances thereof, the power of godliness is manifest.
21 And without the ordinances thereof, and the authority of the priesthood, the power of godliness is not manifest unto men in the flesh;
22 For without this no man can see the face of God, even the Father, and live.
So there we have it. D&C 84 offers us the higher priesthood, but it simultaneously informs us that it is by that means that man can see the face of God the Father, and live. By adding the phrase “and live” it becomes it clear that it is talking about seeing the face of God in mortality. If the phrase had been “in the body” we could decide it meant the resurrection. If the phrase had been omitted we could assume it meant in the spirit world after death. But God chooses to say “and live” so we can have no doubt that he is speaking of mortality. The power of the Melchizedek priesthood is related to seeing God in mortality. This is laid even plainer in D&C 107
D&C 107:18-19 18 The power and authority of the higher, or Melchizedek Priesthood, is to hold the keys of all the spiritual blessings of the church—
19 To have the privilege of receiving the mysteries of the kingdom of heaven, to have the heavens opened unto them, to commune with the general assembly and church of the Firstborn, and to enjoy the communion and presence of God the Father, and Jesus the mediator of the new covenant.
Here we have a more concise statement. That is worth repeating. According to this, the power and authority of the Melchizedek priesthood IS to have the privilege of receiving the mysteries of the kingdom, to have the heavens opened unto them, to commune with the general assembly and the church of the Firstborn, and to enjoy the communion and presence of God the Father and Jesus the mediator of the new covenant.
That is why the Aaronic priesthood does not have power to give the gift of the Holy Ghost. The gift of the Holy Ghost can open up the mysteries of the kingdom. The scriptures have multiple instances where we are told that the spirit of the Lord was upon someone, and because of that they beheld and learned the things of God which are not made known to all men. We read of Christ being carried by the spirit to the pinnacle of the temple and of the spirit of God showing him the whole world. We read:
D&C 76:10 For by my Spirit will I enlighten them, and by my power will I make known unto them the secrets of my will—yea, even those things which eye has not seen, nor ear heard, nor yet entered into the heart of man.
And this is illustrated immediately as the rest of the vision of the degrees of glory starts with these verses:
D&C 76: 11 We, Joseph Smith, Jun., and Sidney Rigdon, being in the Spirit on the sixteenth day of February, in the year of our Lord one thousand eight hundred and thirty-two—
12 By the power of the Spirit our eyes were opened and our understandings were enlightened, so as to see and understand the things of God—
13 Even those things which were from the beginning before the world was, which were ordained of the Father, through his Only Begotten Son, who was in the bosom of the Father, even from the beginning;