The problem (for God) is to harmonise the individual free-wills of a multitude of men. This must be on the one hand a choice, yet on the other hand robust - permanent - if Heaven is to be viable.
It was the work of Jesus to enable free wills to harmonise in this way.
This could not be achieved by The Father - he could only subordinate wills, passively, by obedience to his laws. It could only be achieved by the Son.
This was possible because the real-divine self is universal - and thus selves are 'overlapping', but the incarnated body is capable of genuine agency. In this way, a choice of the real-divine self has universal consequences.
So, while thinking from false, or superficial selves is merely a personal and private fantasy; thinking from the real-divine self is a potentially-universal, shared reality. The 'mechanism' of salvation is consciousness - and by theosis - meaning that it is by becoming divine in our thinking that we attain to permanent salvation, in which state all wills are naturally aligned, because all are thinking from reality.
(Reality being the creation of God.)
In this sense, the mechanism of salvation by the incarnate Jesus, was that Jesus was thinking from his real-divine self, and whatever he achieved in his body was therefore universal.
But this becoming-divine (divination) of consciousness can only be chosen; it cannot be imposed. Thus Jesus need to be incarnated as a Man, to make this free choice.
In contrast, those who take a path of not-thinking, or of obedience merely to the father - and also those who choose a path of amplifying their purely-personal imaginings - cannot move to the level of universal reality that is Heaven.
It is love that enables the move; love that makes people want reality; hence the two great 'commandments' to love God and 'neighbour'. These commandments are not orders to be 'obeyed'; they are an objective description of the choices that are required.
Unless you love God and his creation and also your neighbours - who will dwell with you in Heaven - then you Will Not join it.
We join as individuals; but we then live in-creation with all others who live in-creation.
If you do Not want to live with these others in chosen harmony, because you love them; then you will Not inhabit creation. You will therefore live out-of-creation, in chaos; either consciously alone in your own imagination, or else unconsciously (unaware) alone in chaos (Nirvanah).
Choice is a necessary aspect of free will, which is a fact of existence; the creative harmony of Heaven cannot be imposed but most be chosen - and for Heaven to be harmony it must be chosen for love.