How is Jesus the "Son of God"?

Preamble

There are three main ways Jesus' sonship is conceived:

1. Biological: God is the literal father of Jesus.  This is fostered by the virgin birth infancy narratives (Matthew 1:18-25; Luke 1:26-38) and provides a nice rationale for saying the Jesus is half God and half man/human.
2. Ontological: God is Jesus' father because Jesus shares God's essence or being.  This is fostered by the preexistence passages.
3. Functional: God is Jesus' father because the relationship between God and Jesus mirrors well the human relationship between a father and a son.

I intend to argue that (1) is mistaken, (2) is true, but then the question is why that relationship uses the metaphor of sonship as opposed to some other metaphor such as 'brotherhood'?, and that (3) is both true and instructive.  I contend that most evangelicals tend to view Jesus' sonship only in terms of (1) and (2) and in so doing short shrift (3).  I contend that short shrifting (3) downplays certain qualities of Jesus (and of God) that are crucial both theologically and practically.

Biological sense is mistaken

The infancy narratives do not state that God provided the male aspect and Mary the female aspect of Jesus.

• The first point is obvious.  It is the Holy Spirit that is the agent in Jesus' conception, not God the Father.  Of course, this Spirit is God's spirit and so perhaps this is not a knock down.
• The term "Holy Spirit" is feminine in Hebrew and neuter in Greek, so a reader would not naturally view it as the male contribution to the conception of Jesus.
• The Greek in Matthew 1:18 (she was found to be with child from the Holy Spirit) literally means "in stomach having" which pertain more to being pregnant than becoming pregnant.  Also, the "by" in "by the Holy Spirit" is usually points to the female role in reproduction!  Also, the idiom in verse 20 ("for the child conceived in her is from the Holy Spirit") is not the exactly the idiom used when the male role is meant.  Also, in terms of story line, how would it reassure Joseph to go along with the marriage if paternity is something other than his?
• Luke 1:35 has "the Holy Spirit will come upon you and the power of the Most High will overshadow you", which uses language which is nonsexual.  Parallels for "come upon you" are found in Acts 1:8, Isaiah 32:15 and 1 Samuel 16:13 where sexuality is not at issue.
• "Son of God" language occurs at important junctures in the Gospel if Mark but Mark does not contain an infancy narrative/virgin birth account.  Sonship language in John would also not pertain to (1) but more to (2).  John doesn't have a virgin birth narrative and doesn't show evidence of knowing about it.
• The silence of the virgin birth in the rest of the New Testament and even in Matthew and Luke outside of the infancy narratives (!) make it hard to argue that it was the virgin birth and God's paternity that led to sonship language.

Why is the Ontological sense couched in terms of Sonship?

There is no doubt that according to the New Testament Jesus shares the essence or being of God.  But why would this be couched in terms of Sonship and not, say, brotherhood, for brothers too would share a common essence or being?  It would seem to me that one would have to prove that in Biblical times it was true that a son was viewed as sharing the same essence or being as his father and that perhaps brotherhood could been used instead but simply was not.  I'm not sure how one would prove this but my hunch is that the son-father relationship was not conceived in this way anymore than that a father and son were both male humans etc.  A particular father was simply different than his son.

Functional or metaphorical Sonship

My basic argument here is that sonship language, including 'Son of God' language is based on the special relationship that exists between human fathers and sons.  Once this sense is ignored, very important aspects of Jesus (and of God) are ignored.

• In Biblical times the relationship between a father and a son was special.  A son would often take the vocation of his father and would take after him in other ways.  A son would be obedient to his father and as an heir would continue his father's legacy.  He would try to bring honor to his father by acting in appropriate ways.
• Based on the reality of the first point, there were "son of" idioms which traded on the father-son relationship.  "Sons of Belial" for example does not claim that its referent is the biological offspring of "worthlessness" but that the referent takes after, behave like a personified worthlessness would act.  In the Beatitudes, Jesus calls peacemakers "sons of God" because God is a peacemaker and peacemakers would be behaving like God.  Likewise, in John 8:44 Jesus claims that certain people have the Devil as their father, not because the Devil had sexual relations with their mothers but because they behaved like the Devil.  Compare what he says in John 8:39 that Abraham's children would do the type of things Abraham did.  Paul says something similar in Galatians 3:7, Abraham's children are those who take after him by having his faith. 
• There are many uses of "sons of God" which again trade of the special human relationship between father and son.  Israel (Exodus 4:22), angels (Genesis and Job), Davidic King (2 Samuel 7:14, Psalm 2) and individual Israelites are all called "sons of God" where common essence or being is not at issue.
• There are clear indications that when Jesus is called "Son of God" a Davidic King reference is meant.  For example, when Peter confesses Jesus as Messiah (Davidic King) he add "Son of God".  This is so because God is considered King and so the King of Israel would be acting like God.

Theological Upshot

One aspect of viewing Jesus as "Son of God" in terms of function is that Jesus' obedience to the Father is not forgotten.  Jesus says as much in John 5.  There he says that the Son can only do what he sees the Father doing.  Jesus is clear that he does what the Father does.  Also, the aspect of love is highlighted too.  Just as a human father loves his son, so the the Heavenly Father loves the Son.

We evangelicals ought to have confidence in claiming that Jesus is of the same essence or being as God so we are not afraid to face the human-like aspects of Jesus' relationship to God the Father.  We should not be so wedded to the "Son of God" that we forget the "Son of Man"!