Let's Clarify Terms
Confused yet? Well, let's see what we can do to clarify the situation.
Adam as the Son of God
David as God's Son
David is described in terms of being God's son (2 Sam 7:14 - "I will be a father to him and he will be a son to Me"; Psalm 2:7 - "You are my Son;
today I have begotten you"). Again, the language is metaphorical with God calling David "my son," which is distinct from the terminology of "son of God."
Israel as God's Son
The nation of Israel is also described metaphorically as God's son (Ex 4:22-23 - "Israel is my son, my firstborn son"; Hos 11:1 - "out of Egypt I called my son"; Jeremiah 31:9 - "for I am a father to Israel"). Again, the point is a special designation of the nation of Israel, dedicated to God and to be the recipient of God's promises and inheritance.
The Sons of God (spirit beings) as Sons of God
Aside from Jesus, all the mentions of "sons of God" that I've discussed above are of humans (and even Jesus is human, but he's not just human--he is the Son of God in both his humanity and his divinity). What about the spiritual sons of God (see Job 1:6; 2:1; 38:7 as well as Ps. 29:1; 82:6; 89:6 and Gen 1:26; 3:22; 6:1-4; 11:7)?
The spirit beings who are called the sons of God are ontologically similar to God and Jesus (THE Son of God), but they aren't the same as God. They're spirit beings, and God is spirit, so there's an ontological relationship there, even though only God is God. The sons of God and God Himself can all "fit" under the word "elohim," which is a "place of residence term" (Michael S. Heiser, The Unseen Realm). The terminology "sons" of God mean there's a family inheritance there of some sort--though again we shouldn't presume too much about what that entails or means because we don't have an overabundance of detail about the spirit realm. But here in the OT, we have a categorical designation. Sons of God means that they are not God himself, but there's a class of being whereupon they are similar to God.
What all this similar (and confusing) language means that there is a "spiritual family" that God created and a "human family." In the Old Testament, there is a heavenly host/divine council/royal court that sits in attendance to God and accomplishes his will from the spirit realm (see Psalm 82/Psalm 89/1 Kings 22/Zechariah 3/Job 2-3). But in the Old Testament, the particular designation of "sons of God" (Hebrew: bene elohim) is a term for ontological spirit beings. Not humans.
If you look at the Hebrew of the OT, neither Adam, nor David, nor Israel as a nation, is called bene elohim. Rather the term "son" is used metaphorically. For instance, in 2 Sam. 7:14, it says of David, "I will be a father to him and he will be a son to Me." The nation of Israel is likewise metaphorically called God's son, as in Exodus 4:22 where it says, "Israel is My son, My firstborn."
The Hebrew term "sons of God" is reserved for spiritual beings. (Gen. 6:2, 4; Job 1:6; 2:1, 38:7; Deut 32:8 (LXX). Psalm 29:1 and 89:6 use the construct bene elim. Psalm 82:6 uses bene elyon. The only other place we see the construction "son of God," this time in the singular, is with the fourth figure in the furnace in Dan. 3:25, which most Christians understand as a theophany, or a preincarnate appearance of Jesus. Even if this is somehow not Jesus, that figure is clearly a spiritual being.)
Believers as Sons of God
12 But as many as received Him, to them He gave the right to become children of God, even to those who believe in His name,
13 who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
14 For all who are being led by the Spirit of God, these are sons of God.
26 For you are all sons of God through faith in Christ Jesus.
5 so that He might redeem those who were under the Law, that we might receive the adoption as sons.
6 Because you are sons, God has sent forth the Spirit of His Son into our hearts, crying, “Abba! Father!”
7 Therefore you are no longer a slave, but a son; and if a son, then an heir through God.
1 Corinthians 6:3 (NASB95)
3 Do you not know that we will judge angels? How much more matters of this life?
21 ‘He who overcomes, I will grant to him to sit down with Me on My throne, as I also overcame and sat down with My Father on His throne.
26 ‘He who overcomes, and he who keeps My deeds until the end, TO HIM I WILL GIVE AUTHORITY OVER THE NATIONS;
27 AND HE SHALL RULE THEM WITH A ROD OF IRON, AS THE VESSELS OF THE POTTER ARE BROKEN TO PIECES, as I also have received authority from My Father;
12 If we endure, we will also reign with Him; If we deny Him, He also will deny us;
Saints/holy ones language, NT and OT:
The New Testament frequently refers to God's people as "saints" or "holy ones." This designation appears in several books:
Romans 1:7
7 To all in Rome who are loved by God and called to be his holy people.
1 Corinthians 1:2
2 To the church of God in Corinth, to those sanctified in Christ Jesus and called to be his holy people.
Ephesians 1:1
1 To God's holy people in Ephesus, the faithful in Christ Jesus.
Colossians 1:2
2 To God's holy people in Colossae, the faithful brothers and sisters in Christ.
Acts 9:13
13 But Ananias answered, “Lord, I have heard from many about this man, how much evil he has done to your saints at Jerusalem.
Revelation 5:8
8 And when he had taken the scroll, the four living creatures and the twenty-four elders fell down before the Lamb, each holding a harp, and golden bowls full of incense, which are the prayers of the saints.
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Who are the holy ones in the OT?
Psalm 89:5-7
5 The heavens will praise Your wonders, O LORD; Your faithfulness also in the assembly of the holy ones.
6 For who in the skies is comparable to the LORD? Who among the sons of the mighty is like the LORD,
7 A God greatly feared in the council of the holy ones, And awesome above all those who are around Him?
Daniel 4:17
17 The sentence is by the decree of the watchers, the decision by the word of the holy ones, to the end that the living may know that the Most High rules the kingdom of men and gives it to whom he will and sets over it the lowliest of men.
Let's Summarize!
With all these passages brought to bear, what can we say about the sons of God from the OT to today?
- The "sons of God" in the Hebrew construct are a class of beings who are similar to (but dependent on) God, meaning they are spiritual beings.
- The metaphor of "God's son" is used for both David and the nation of Israel.
- Adam is called "the son of God" in Luke.
- Believers are the "new" sons of God in the New Testament. This has associations with the holy ones/the divine council of the Old Testament. (Note: we don't know what this fully means; we should not presume that all the spiritual sons of God are demoted/removed in place of humans...this seems unlikely because the destiny of humans is to be on the New Earth, so surely God's spirit progeny will remain in the New Heavens.)
- Associated with the concept of believers being the sons of God is that they are sanctified/conformed into the image of Christ.
Regarding my starting question:
The saints/believers are for sure children of God. Humans at large can certainly take the designation in a metaphorical way, because God is our Father and our Creator and the One who made us and provides all things for us. We are all of one human family.
But, in Christian circles we rarely hear of the designation "child of God" to reference all of humanity, because the NT uses such language to designate followers of Jesus. (This isn't to say that you don't ever hear it from Christians; see above about us being all one family!)
The moral of all this is not that Christians should be putting ourselves into an elevated position compared to the other imagers of God, but rather that we should be working to bring everyone under the same family where we can all partake of the inheritance offered to us through Christ.
Another great take-away is that this demonstrates the beauty of understanding the bible in context. Yes, there's a "disconnect" in meaning from OT to NT, but there is also a continuity, and the continuity is seen within the disconnect. Understanding who the sons of God were originally helps us see the meaning behind the sons of God today. (And by the way, all this stuff is partially why the human rulers/Sethite view came into such vogue in the church, because suddenly the sons of God couldn't be divine rebels since, hey, we know that the sons of God are in the church!)