I’ve been growing lately in my understanding of how the term “son of God” is used across the canon. In the beginning, God creates Adam in his image to represent him and rule creation (Genesis 1:26-28). Part of the meaning of creation in God’s image, in my opinion, is that we are God’s children. To be “in his image, after his likeness” is to be a in a Father-son relationship with him.
“When God created man, he made him in the likeness of God. Male and female he created them, and he blessed them and named them Man when they were created. When Adam had lived 130 years, he fathered a son in his own likeness, after his image, and named him Seth.”
“Enos, the son of Seth, the son of Adam, the son of God.”
Then when Adam falls into sin and fails at his task, God calls Abraham/Israel into covenant relationship and promises the redeem the world through them. This people is also called the firstborn son of God (Exodus 4:22-23). David, their king and representative, takes on this title as well (II Samuel 7:14, Psalm 2:7, Psalm 89:26-27, cf. v. 20). But Israel falls into idolatry and exile, and David’s rule is temporary and disappointed. Neither Israel nor David redeems the world.
Then comes Jesus, about whom God says, “You are my beloved Son; with you I am well pleased” (Mark 1:11). Although at times the term “Son of God” is used in the New Testament to refer to Jesus’ eternal status as the second member of the Godhead, at other times it used as a messianic title, indicating not that Jesus is divine but that he is Davidic, and recalling the whole swath of biblical connotations outlined above. For example, Nathaniel’s statement of belief in John 1:49 couples “the Son of God” with “the King of Israel.” Martha calls Jesus “the Christ, the Son of God, who is coming into the world” in John 11:27. The high priest commands Jesus in Matthew 26:43, “tell us if you are the Christ, the Son of God.” The apostles make this same connection between “Christ” and “Son of God” (John 20:31, Acts 13:33).
My conclusion: “Son of God” in biblical theology = Adam —> Israel —> David —> Christ, who is the last Adam (Romans 5, I Corinthians 15), the true Israel (Matthew 2:15), and the better David (Ezekiel 37:24, Luke 1:32-33).