Course XXXVI - Teaching 16: Descent to Earth

In higher planes, souls enjoy a limpid and free spiritual atmosphere. Nothing penetrates into those very high regions where beings shire and scintillating stars.
But when those beings spiritually more advanced had exhausted their spiritual wealth that caused them to dwell in the first plane of the Astral world, a vague desire of action starts stopping the wonderful rotation of its lights. Memories of love and life mixed with peace of the environment drive them to return to the material plane. A very deep sleep of some kind wraps these souls, which weakens gradually their shine.
Like new sleeping Walkiries by the voice of love, they descend from the mental planes and concentrate the whole strength of their consciousness on the first plane of the Astral world
Also the eagerness of the soul, of less evolves beings, gets there before their reincarnation, to concentrate the powers of the new life, which has to act on Earth (Third plane).
From there, they descend to the second and the third Astral plane, where all possibilities of the souls join with mental factors left behind during their ascension. Now they are fit to human life.
In successive astral planes, these souls cover themselves with the energetic and astral body, and are fit for the mission he has to develop in the world.
In the seventh Astral plane, low instincts, evil deeds unpaid, which form their ethereal body that is the definite mould of the physical body, are waiting for them. They must fight, begin and see how life drips from their hands, just leaving behind drops of memories.
It is the hour of hours, the solemn time of sacrifice and crucifixion; a divine spirit nailed on the cross of flesh.
In vain these souls tried to be free forever. Destiny calls, forces and pushes, and from the heights of divinity, a being has to descend into the shadow of matter.
All those who are on Earth have enjoyed a perfect peace for a longer or shorter time according to their spiritual progress; but a true liberation, by breaking any desire, puts the soul in contact with the universal serenity that is eternal.