Question: Why was the Son called God by God?
Answer: Because the Son inherited the highest name of His Father (Heb 1:4, Philippians 2:9-10, John 17:11, John 5:43) but the Son is also part of the creation, the cornerstone of the creation and salvation, pre-eminence in all sense of pre-eminence, first in all sense of first, first to have given a life in time to which through Him all came to be, first to be resurrected with a glorified body (Col 1:15-16). He was the only one who has the fullness of God bodily (Col 2:9), fullness in a sense that the full quality of God’s essence is in the Son.
The Son serves as the Image of the invisible God who on behalf of the Father took care of the creation. The Son who was also called God by God who created Him was the one who speaks in Gen 1:26, the one walking in Gen 3:8, the one who Moses face to face in Exodus 33:11, who was called Angel of the Lord in Act 7:35, the one seen by Jacob in Gen 32:30. He was the root of David since it was through Him that Man was made and also the descendant of David (Rev 22:16) because it was Him who came in flesh- the chosen man or Christ who speaks on the last days (Heb 1:2). In 1 Tim 3:16, the God that manifested in the Flesh was not the Father but the Son who God Himself called God.
All in all, there is only ONE God in the name JESUS, He is ETERNAL LIFE Himself and His first-ever creation was His Image (Son) who obtained by inheritance the name Jesus but was revealed only in the right season (Ecc 3:1-8). This right season was when the Son became the Christ.