God could not have redeemed people, that is, rescued them from damnation and hell, without first taking on a human manifestation. There are many reasons for this; they will be disclosed step by step in what follows. Redemption was a matter of gaining control of the hells, restructuring the heavens, and then establishing a church. Despite his omnipotence, God could not accomplish these things except through his human manifestation, as one cannot do work without arms. In fact, in the Word his human manifestation is called the arm of Jehovah (Isaiah 40:10; 53:1). By analogy, one cannot attack a fortified city and destroy the temples of idols there without powerful means.
The Word as well makes it clear that having a human manifestation gave God the omnipotence to do this divine work. God is in the inmost and purest realms. There was no other way he could cross over to the lowest levels where the hells exist and where people were at that time, just as a soul cannot do anything without a body. By analogy, there is no way to overpower enemies who are not in sight and whom we cannot get close to with weapons such as spears, shields, or guns.
To redeem people without a human manifestation would have been as impossible for God as it would be for someone [outside India] to take control of people in India without sending in troops on ships. It would be as impossible as growing trees on heat and light alone if air had not been created as a medium through which they travel and earth had not been created in which the trees could grow. In fact, it would be as impossible as catching fish by throwing a net in the air and not in the water.
Given Jehovah’s inherent nature, despite his omnipotence he could not touch any individual devils in hell or any individual devils on earth and control them or their rage or tame their violence unless he could be as present in the farthest realms as he is in those closest to him. In his human manifestation he is in fact present in the farthest realms. This is why the Word refers to him as the First and the Last, the Alpha and the Omega, the Beginning and the End [Revelation 1:8, 11; 21:6; 22:13].
from True Christianity, Section 84