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.
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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.
2nd.
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.
3rd.
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.
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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.
(DHC 5:554-556)