No one who understands the central doctrines of any of the world's leading religions should have any difficulty understanding Kant, because his philosophical vision is congruent with the teachings of Hinduism, Buddhism, Islam, Judaism, and Christianity. It is a shared doctrine of these religions that the empirical world we humans inhabit is not the only world there is. Ours is a world of appearances only, a transient world that is dependent on a higher, timeless reality. That reality is of a completely different order from anything that we know, it constitutes the only permanent reality there is, and it sustains our world and presents it to our senses. Christianity teaches that while reason can point to the existence of this higher domain, this is where reason stops: it cannot on its own investigate or comprehend that domain. But one day, it is promised, when our earthly journey is over, we will know the higher realm and see things as they really are.
This passage is a good illustration of why Kant is an unfortunate choice for a Christian philosopher. While other religions may offer hope of escape into a higher realm, the specifically Christian hope is resurrection and everlasting life in this world. Why would Christ suffer and die on a Cross only to be resurrected into a world of mere appearance? No, the Christian cannot hold that this world is a transient world of mere appearance on pain of making nonsense of the Gospel.
The Christian world is not a divided world of appearance vs reality, or transient worlds vs permanent worlds. God created man, body and soul, in form a rational animal. A rational animal is not a soul trapped in a body ala Plato, or a rational principle discovering it lives in a world of illusion ala Kant, but a unity of body and soul created specially for the purpose of knowing. When man dies, he really dies: It isn't birth into a higher realm, but a genuine loss of being. The separated soul survives, and God can and does infuse it directly with knowledge; but the soul by nature desires to exist in unity with the body of which it is the form. When man in his fullness is resurrected, once again does the soul know in its natural mode - through the senses. And what it knows is reality, not a shadowplay constructed by God to fool all but the cleverest philosophers.