There is a clear teaching in ACIM that there are TWO worlds, and you can ONLY see one of the two in its entirety at any given time. Seeing one, REQUIRES you NOT TO SEE the other. You CANNOT see both of them in full simultaneously. And each of them uses a different KIND of vision, designed ONLY to see one kind of world.
One of these two worlds is Earth and its environment - all galaxies etc. The other is the real world/heaven - God's creation. You can ONLY see ONE of the two in full. If you shift your vision to true perception you can see God's world. If you shift your vision to false perception you can see the physical world. But you CANNOT DO BOTH AT ONCE.
So there is a dynamic, whereby the MORE that you see the real world, the LESS you see the physical world. As the real world "phases in", the physical world "fades out". You cannot see both at once, and in order to see one or the other you have to sacrifice the ability to see its opposite.
To the DEGREE that you value one of the worlds, that is how much you will see it, and inversely, this valuing of it causes you NOT TO VALUE the opposite world, which causes you to SEE IT LESS. This is a basic function of perception, that you see what you value, because you believe in it, and thus want to see it. You do NOT SEE what you DO NOT VALUE. And any world you consider "false" due to its opposite being "true", becomes invisible to you.
This is a very core teaching. You are choosing between heaven or hell.
"The world is false perception" and relies on physical sight of photons using the biological apparatus of the eyeballs an nerves etc.
The real world is true perception/christ vision and relies on the spiritual eye, which in turn DOES NOT rely on the body, and is direct mind-seeing.
Two types of perception. Two ways of seeing. Two worlds resulting. "The alternating investment in the two types or levels of perception is usually experienced as conflict for a long time, and can become very acute."
"This world you see MUST BE DENIED, for sight of it is costing you a different kind of vision. YOU CANNOT SEE BOTH WORLDS. For each of them involves a different kind of seeing, and depends on what you cherish. The sight of one is possible because you have DENIED THE OTHER."
"Both are not true, yet either one will seem as real to you, as the amount to which you hold it dear"
"Eventually, everybody begins to recognize, however dimly, that there MUST be a better way. As this recognition is more firmly established, it becomes a perceptual turning-point. This ultimately reawakens the spiritual eye, simultaneously weakening the investment in physical sight."
""The real world can ACTUALLY BE PERCEIVED. All that is necessary is a willingness to perceive nothing ELSE. For if you perceive both good AND evil, you are accepting both the false AND the true, AND MAKING NO DISTINCTION BETWEEN THEM."
"Accept the one illusion which proclaims there is no condemnation in God's Son, and Heaven is remembered instantly; the world forgotten"
"The world stands like a block before Christ's face. But true perception looks on it as nothing more than just a fragile veil, so easily dispelled that it can last no longer than an instant. It is seen at last for only what it is. And now it cannot fail to disappear."
"When the thought of separation has been changed to one of true forgiveness, will the world be seen in quite another light; and one which leads to truth, where all the world must disappear."