1. Human beings, in general, are called ‘Gods children.’ God creates us and sustains us. Just as a human father provides for his family, God also provides for us, though much more in a significant way.

Acts 17:28 (NIV)
‘For in him we live and move and have our being.’ As some of your own poets have said, ‘We are his offspring.’

 2. Spirit beings like the angels are called the Sons of God because God sustains them and cause of their roles in carrying out God’s command. 

Job 1:6 (NKJV)

Now there was a day when the sons of God came to present themselves before the Lord, and Satan also came among them.

3.The nation of Israel is called ‘God’s son.’ The development of the nation of Israel was not like the other nations; God produced it through divine intervention and was, therefore, Israel’s Father.

Exodus 4:22 (NIV)
Then say to Pharaoh, ‘This is what the Lord says: Israel is my firstborn son,

King David was called the Son of God because he was put on the throne by God and ruled under God’s authority as God’s representative. 

So the phrase the Son of God can have various meanings, but why then do Christians insist on calling Jesus the Son of God?  

Jesus is the Son of God in the divine sense by His position in the Trinity. 

In the first century, most people thought of the son as someone who carried on the family trade. Sons did not go to college; they did whatever their fathers did. If your father was the butcher, you became butcher, and if your father was a baker, you worked as a baker.  

To say that Jesus was the Son of God in this sense would mean to say that He does the work of the Father, and this is what Jesus claimed about Himself. 

According to the Bible:

• God is the one who raises people from the dead and Jesus claimed He will raise the dead at the resurrection.
• God is the final judge of all mankind and Jesus tells the disciples that He will be the final judge of all people.
• God is the only one who could ultimately forgive sins and Jesus openly forgave the sins of people who approached Him while on earth.

So Jesus does the works that the Father does, and the only way someone can do the same job as the Father is if He shares the same nature and attributes as the father.  Jesus claimed to have this unique relationship with the father. 

Matthew 11:27 (NKJV)

All things have been delivered to Me by My Father, and no one knows the Son except the Father. Nor does anyone know the Father except the Son, and the one to whom the Son wills to reveal Him.

Because Jesus is the supreme Son of God, He is the best example of all the above-mentioned ‘Sons of God.’  

The Spirit beings are called Sons of God, but Jesus is the highest spiritual being. Human beings are called Sons of God, but Jesus was the greatest human being that ever lived. The Davidic kings were called Sons of God, but Jesus was the Messiah, the eternal Davidic king. The nation of Israel was called the Son of God, but Jesus is the promised Messiah (Savior) of Israel and the whole world.