There are two worlds, because God created one world, and then you went and tried to make another world to oppose His Kingdom.
This second world is this universe, including the Earth. It is OPPOSITE in nature to God's Kingdom in EVERY way. And here is a key, CORE FACT in the A Course in Miracles metaphysics. YOU CANNOT SEE BOTH OF THEM AT ONCE.
In order to see Earth, which includes bodies, and the world around you, you HAVE TO BE BLIND to Heaven. There is nothing so blinding as sight of form. To feast your eyes upon forms, objects, buildings, cars, houses, and bodies, you MUST have denied Heaven. And that means you believe sin is real, have made it real, and are now seeing it.
This is also why "to see a sinless body is impossible", because the ONLY way to see a body AT ALL is to believe in sin, which denies sight of Heaven and shows you the world you made.
Now, it should be fairly clear that there are NO EXCEPTIONS to this rule. You CANNOT see Heaven if you are seeing Earth. Jesus says that the WAY you see each one is so DIFFERENT, it requires an entirely different KIND of vision, and the two kinds of vision are completely incompatible. If you have one of the kinds of vision, it BLOCKS the other kind of vision.
This is a pivotal fact. Either you will see the Earth, OR you will see Heaven. But you will NOT EVER see both together. This is also why it is IMPOSSIBLE to merge Heaven and Earth and to have "heaven on earth", as if you are experiencing BOTH at the same time. You cannot. Their NATURE is completely opposite. The Earth's nature KEEPS IT APART from Heaven permanently. It OPPOSES Heaven and its three-dimensional space-time-dependent nature is completely incompatible with Heaven's laws.
So you have a choice to make. Either you want to see Earth, or you want to see Heaven. YOU CANNOT HAVE BOTH.
There is, however, temporarily, a transitionary period, in which you are learning to look AWAY from the Earth, and towards Heaven. This is the process of learning to let go of the "false perception" body-based existence that YOU MADE, and learning the Holy Spirit's alternative dream, the re-interpretation of what you made, which BEGINS to reveal to you two important facts which are OPPOSITE to what you taught yourself:
1) Earth is NOT REAL, it's an illusion, and you are learning to look THROUGH it and PAST IT. That is what forgiveness means.
2) Heaven IS REAL, it's reality, and you are learning to see it BEYOND this world, BEHIND forms and objects, which is what it means "God is in everything I see". It is not talking about a final state of God being 100% in everything you see, it's talking about a transitionary state where you MOSTLY see God in everything you see IN SPITE OF everything the body looks at.
Once you have reached the maximum level of true perception in which the body's eyes STILL show you false perception, a world of sin and death, with people suffering and dying, but simultaneously see a light BEYOND it, to such an extent that all the illusions of the world FAIL to TEMPT you to believe they are REAL, the world - Earth - becomes nothing but a thin veil over the face of Christ. It becomes so literally thin that you can see through it, because you are transcending physical matter.
At that point, you are as ready as you CAN be in a dream, in a body, having a kind of double-vision, where the world has almost disappeared and you are almost entirely aware of Heaven. God then takes the final step.
In this final step, your experience of Earth existing ENDS. This is where you go 100%! This is where your sight of Heaven becomes TOTAL, and your blindness by form becomes 0%! You no longer see bodies, you no longer see the world, and there is no world. You are now IN HEAVEN. In reality. In truth. And in this truth the alternative world - Earth - has completely vanished.
You cannot have your cake and eat it. You either get to have Earth, or you get to have Heaven. "Heaven is a choice I must make". All your efforts to make Earth BE heaven is futile. It's like trying to turn something false, that will always be false, into something true. You CANNOT SUCCEED. To do so would make the world REAL, and destroy Heaven.
The physical aspect of what your body sees is supposed to be OVERLOOKED and no longer register as real. It seemed real to you when you had FALSE PERCEPTION. False perception means you are looking AT an illusion, IN an illusory way, thus a double illusion, in which you believe that the illusion "out there" (the world, Earth) is REAL, when in fact it is just an illusion. Your illusions ABOUT IT need correcting, so that you can stop believing that the illusion OUT THERE is reality.
In true perception you will come to recognize this world IS NOT REAL, and is an illusion, and you will have no further illusions ABOUT IT being reality. Teachers of God look upon the world and ARE NOT DECEIVED by what they see, because what they see is NOT REAL. The body's eyes continue to show you LIES, SINS, HATE, DEATH. It has no choice to see anything but this. And so you HAVE TO learn to stop believing what your body tells you is real. You have to overlook it. See PAST it with reason. Look BEYOND the veil to reality. Reality is NOT the Earth, Earth is a lie.
You cannot see two worlds. You cannot see Heaven while you are in a body. You can PERCEIVE a REFLECTION of Heaven AT THE SAME TIME as perceiving bodies still. THAT IS NOT HEAVEN. To see bodies is to see SIN. Bodies must go. Only when you are done with bodies, done with perception, and done with the illusory world, COMPLETELY, will you be willing to be IN HEAVEN with God where you belong.
And then, there is no world.