D&C 83 - 84

The priesthood is an order of men, an order "...after the holiest order of God." (Doctrine and Covenants Section 84:18) Not an order of all men, but an order of those who choose to be "faithful" (Doctrine and Covenants Section 84:33), and desire "...to be a greater follower of righteousness, and to possess a greater knowledge, and to be a father of many nations, a prince of peace, and desiring to receive instructions, and to keep the commandments of God..." (Pearl of Great Price Abraham 1:2)

For I see three purposes of this priesthood order -

1) "..this greater priesthood administereth the gospel and holdeth the key of the mysteries of the kingdom, even the key of the knowledge of God." (Doctrine and Covenants Section 84:19) It is through this order through the presidents and presidencies with administering keys that revelations flow, instruction and counsel is given, members are reproved, rebuked, and admonished in love and righteousness. It is through this order that fathers teach their families and individual revelations and testimonies are received by the Spirit.
2) "...in the ordinances thereof, the power of godliness is manifest." (Doctrine and Covenants Section 84:20) It is in the authority of this order that ordinances are performed, members receive the Holy Ghost, and promises, blessings, and gifts are bestowed to the witness of all.
3) "...without this no man can see the face of God, even the Father, and live." (Doctrine and Covenants Section 84:22) For it is through this order that we come to learn and understand the principles of the gospel and the will of the Lord. It is through this order that essential ordinances and covenants are administered and received. And it is because of this order that we are sanctified as "Moses sought diligently to sanctify his people that they might behold the face of God;" (Doctrine and Covenants Section 84:23) for is was "...them who are sanctified before his throne, worshiping God, and the Lamb..."(Doctrine and Covenants Section 76:21) that the Prophet witnessed were before the face of God.

And regarding this order, there are really only three choices men have -

Those that are "...faithful unto the obtaining these two priesthoods [Aaronic and Melchizedek) of which I have spoken, and the magnifying their calling... " (Doctrine and Covenants Section 84:33). To those the promises are that they will be -

"sanctified by the Spirit unto the renewing of their bodies.
34 They become the sons of Moses and of Aaron and the seed of Abraham, and the church and kingdom, and the elect of God.
35 And also all they who receive this priesthood receive me, saith the Lord;
36 For he that receiveth my servants receiveth me;
37 And he that receiveth me receiveth my Father;
38 And he that receiveth my Father receiveth my Father's kingdom; therefore all that my Father hath shall be given unto him.
39 And this is according to the oath and covenant which belongeth to the priesthood.
(Doctrine and Covenants Section 84:33 - 39)

And it is an "...oath and covenant of my Father, which he cannot break, neither can it be moved." (Doctrine and Covenants Section 84:40)

The second choice is receive this priesthood and choose to not magnify my calling - for he that "...breaketh this covenant after he hath received it, and altogether turneth therefrom, shall not have forgiveness of sins in this world nor in the world to come." (Doctrine and Covenants Section 84:41)

That last choice is to not even become part of the order at all. To that the Lord said -

"And wo unto all those who come not unto this priesthood..." (Doctrine and Covenants Section 84:42) To me, the word "wo" is sufficient.

My choice is the first and to do so, I need "to beware concerning [myself], to give diligent heed to the words of eternal life.
44 For you shall live by every word that proceedeth forth from the mouth of God.
(Doctrine and Covenants Section 84:43 - 44)