Unlike a servant who can resign or be sacked, a son abides in the house forever (-John 8:35), under the shadow of the almighty (-Psalm 91:1), with goodness and mercy surely following (-Psalm 23:6).
Being just a visitor that only comes into the presence of the master when he is needed, the servant does not see everything the master does, whereas, the son even sees ahead, and knows what God is going to do. -John 5:20
Being a son of God is superior to just being His servant.
“God called Job "My servant", little wonder he allowed Satan to experiment with him (Job 1:8-12); My father will never permit the enemy to experiment with my health, resources or anything that concerns me because I am His son.”
Memorise: I will be his father, and he shall be my son: and I will not take my mercy away from him, as I took it from him that was before thee: -1 Chronicles 17:13 
