Who are the sons of God? And what is their purpose?

“For the anxious longing of the creation waits eagerly for the revealing of the sons of God.” Romans 8:19  The longing of creation is for its regeneration. The chosen instrumentality of God for this purpose is a royal priesthood - that is kings and priests.

Then he said, "These are the two anointed ones (sons of the oil) who are standing by the Lord of the whole earth." Zechariah 4:14 Literally they are Joshua the Priest and  Zerubbabel the Prince.  It is not so much who they were, but what they are. They are the implements of God to establish the place of His Presence in the earth with a view to the regeneration of all things - both in the heavens and on the earth.  

Shekinah 

Of course it was under them that the Second Temple was built - but it had not the Presence of God as the First Temple had under Solomon. Yet it was a harbinger of the day when the Shekinah of God would enter its chambers in the Person of the Son of God.  Still in the purpose of God it had to be laid low as it was in 70AD so that the people of God would no longer mistake a building for the true residence of His Presence which was to be His people - “But you are a chosen race, a royal priesthood, a holy nation, a people for his own possession, that you may proclaim the excellencies of him who called you out of darkness into his marvelous light.” 1 Peter 2:9  

Jesus said to them, "Truly I tell you, at the renewal of all things [regeneration], when the Son of Man sits on his glorious throne, you who have followed me will also sit on twelve thrones, judging the twelve tribes of Israel.” Matthew 19:28

There was a brief glimpse of this 160 years before Christ under the Maccabean dynasty who served both as priests and kings - but it was only a foreshadow of what was to come. “The hundred-year reign of the Maccabean priest-kings may be seen as a distant cousin of the thousand-year reign of the Messiah’s people, the “reigning priesthood,” in Revelation 20:6.” Wright, N. T.. The Day the Revolution Began (p. 128). HarperOne. Kindle Edition. 

Please understand that this reference is not about a futuristic period of time - but about the present reality of the Messiah’s current reign.  The number 1000 signifies infinity - a rule without end. As to the Book of the Revelation it is a benediction - the bestowing of a blessing.  "The kingdom of the world has become the kingdom of our Lord and of His Christ; and He will reign forever and ever." Revelation 11:15  

(This was a kind of John the Baptist era (intertestamental) - preparing the way for the ‘Millennial’ Kingdom.  For his father was a priest and his mother was of the Davidic line - a king.)  

Reign 

“and made us kings and priests to our God, and we will reign on earth."  Revelation 5:10 “the future of redeemed mankind is not one in which the earth is discarded or eliminated. As the earth is an integral part of God’s creation, the renewal of creation includes the new earth as well as the new heaven.”  Philip E. Hughes

The Reign of Christ is authenticated by Kings and Priests.  They represent its present reality.  This is just not about restoration which is looking back to the way things used to be - but about regeneration, looking forward to the way things will become. “But in keeping with his promise we are looking forward to a new heaven and a new earth, where righteousness dwells.” 2 Peter 3:13 

“In the exercise of His will He brought us forth by the word of truth, so that we would be a kind of first fruits among His creatures.” James 1:18

There is no greater witness to God's goodness than that which is written upon the dome of heaven, even the regeneration of man. As the old creation was "by the Word" (John 1:3; John 1:10, et seq.), the new is by Him also, the Logos, the Word of Truth, and that by means of His everlasting gospel, delivered in the power of the Holy Ghost. So tenderly is this declared, that a maternal phrase is used--God brought us forth in the new birth; and though "a woman" may forget "the son of her womb" (Isaiah 49:15), yet will He "never leave, nor forsake" (Hebrews 13:5).  Charles Ellicott 

Oneness

The two - sons of the oil - must work hand in hand for they are one in purpose.  “to the building up of the body of Christ; until we all attain to the unity (oneness) of the faith, and of the knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ.” 

As Christ prepared to arise from the Covenant Table of Blessing this petition burst forth from His soon to be wounded heart to the Ancient of Days. “I do not ask for these only, but also for those who will believe in me through their word,  that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us, so that the world may believe that you have sent me. The glory that you have given me I have given to them, that they may be one even as we are one,  I in them and you in me, that they may become perfectly one, so that the world may know that you sent me and loved them even as you loved me.” John 17:20-23

Oneness is a function - not just a demonstration.  It is organic - not organizational.  It is of the heart - not of the head.

Our purpose is singular - one!  That is to be image-bearers of the First Born of all creation. “For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren;” Romans 8:29 

“the reign of the infinitely gracious Jehovah is the hope of mankind, and when they all yield to it the race will have its paradise restored. The very globe itself may well be glad that its Maker and liege Lord has come to his own, and the whole race of man may also be glad, since to every willing subject Jesus brings untold blessings.” The Treasury Of David - C.H. Spurgeon

Soli Deo Gloria!