A Son is given

Isaiah 9:6

For unto us a Child is born,
Unto us a Son is given

A child is born, a son is given, why not a son born? What's the difference?

Psalm 2 speaks of God's anointed becoming king and God pronouncing the begetting or the giving of a son. The king speaks and says:

7. I will tell of the decree:

The Lord said to me, You are my Son;

today I have begotten you.

 A child is born and a king is decreed! The King that will inherit the nations and crush them with a rod of iron. This giving of a Son is the key to the relationship with God, it's through the Son our relationship with God will be judged. 

11 Serve the Lord with fear,

and rejoice with trembling.

12 Kiss the Son,

lest he be angry, and you perish in the way,

for his wrath is quickly kindled.

It's not simply the birth of a child but the giving of a Son, the Son of God, King of Kings and Lord of Lords.