Gary: A Course in Miracles (ACIM ) is saying that of the two seeming worlds; one being the world of God and two, being the world of man, that only the world of God is true because it is a nondualistic system.
There may seem to be two worlds but in fact there is really only one. Some mistakenly believe that A Course in Miracles is a dualistic system because it talks about both. What it says is that only one is true which is Heaven; it is actually a non-dualistic system. This makes it different from virtually all other spiritual teachings in the world. Most spiritual teachings have God creating something other than Himself and then interacting with it.