By Elias Ayala (MDiv & M.A.T.)
No! God did not change his nature because God cannot change his nature. God in his essence is immutable; that is, God does not change. This is the clear teaching of the Bible: “For I the Lord do not change; therefore, you, O Children of Jacob, are not consumed” (Malachi 3:6). An important aspect of God’s immutability (unchangeableness) is that not only does God’s nature not change, but because he does not change we can trust in his promises, since for God to change his mind regarding them would entail a change in God. At that point, God would be engaged in lying which is an activity that scripture teaches is impossible for God to engage in (Hebrews 6:18).
Consider the following: The physical universe is always undergoing change, however, since God is not bound by physicality, he is not subject to the change that the physical cosmos undergo. As a non-material Spirit (John 4:24), God does not have acting upon him the laws of entropy and decay. A spirit is not subject to physical decay since a spirit is of a different nature than that which is physical.
Within biblical theology, Christianity teaches that God is a Trinity. The doctrine of the trinity is the teaching that there is One God who exists as three Persons, Father, Son, and Holy Spirit. This teaching is strict monotheism since it does not affirm that there are three beings. Rather, there is One being who exists as three coequal and coeternal Persons. The Trinitarian distinction between “Being” and “Person” is very important.
When the 2nd Person of the Trinity took on human flesh and dwelt among us (John 1:14), the Triune God’s nature was not changed. In the essence of the triune God, nothing changed. Rather, the Second Person of the trinity took onto himself a human nature. This taking on of a human nature did not in any way change the divine nature. The biblical doctrine of Christ is that in the “1” Person of Jesus Christ dwelt “2” distinct natures both human and divine. These natures are not intermingled with each other but hold distinctly within the “1” Person. As mysterious and difficult as that may seem, it is false to suggest that when the 2nd Person of the trinity took on human flesh, that the nature of the triune God was changed in the process.
In closing then, the nature of the triune God did not change when the 2nd Person took on flesh.