There are two things for which the Lord came into the world and through which he saved people and angels: redemption, and the glorification of his human aspect. These two things are distinct from each other, but they become one in contributing to salvation.
In the preceding points we have shown what redemption was: battling the hells, gaining control over them, and then restructuring the heavens. Glorification, however, was the uniting of the Lord’s human nature with the divine nature of his Father. This process occurred in successive stages and was completed by the suffering on the cross.
All of us have to do our part and move closer to God. The closer we come to God, the more God enters us, which is his part. It is similar with a house of worship: first it has to be built by human hands; then it has to be dedicated; and finally prayers are said for God to be present and unite himself to the church that gathers there.
The union itself [between the Lord’s divine and human natures] was completed by the suffering on the cross, because this suffering was the final spiritual test that the Lord went through in the world. Spiritual tests lead to a partnership [with God]. During our spiritual tests, we are apparently left completely alone, although in fact we are not alone—at those times God is most intimately present at our deepest level giving us support. Because of that inner presence, when any of us have success in a spiritual test we form a partnership with God at the deepest level.
In the Lord’s case, he was then united to God, his Father, at the deepest level. The Lord was left to himself during the suffering on the cross, as is clear from his crying out on the cross: “God, why have you abandoned me?” [Matthew 27:46]. This is also clear from the following words spoken by the Lord: “No one is taking my life away from me—I am laying it down by myself. I have the power to lay it down and I have the power to take it up again. I received this command from my Father” (John 10:18).
From the points just made it is clear that it was not the Lord’s divine nature that suffered, it was his human nature; and then the deepest union, a complete union, took place.
An illustration of this is that when we suffer physically, our soul does not suffer, it merely feels distress. After victory, God relieves that distress and washes it away like tears from our eyes.
from True Christianity, Volume 1, Section 126