CAN YOU CHANGE YOUR PERCEPTION?
While it may seem in many ways that ACIM is telling you to change your perceptions, you can't actually do this by changing your perception.
"Projection makes perception" tells you that perception is caused by projection. This statement confirms it.
"Perception is a RESULT, not a cause."
Which means that perception is an EFFECT. And you cannot change effects without changing their causes. The cause of perception is projection. Which tells you that you need to change WHAT you project, in order to change what you perceive.
"The world IS perception" and "The world is effect" tells you the same thing. You project a world as an EFFECT, not as something causal, and changing your perception does not cause anything.
However, in the question of what you project, projection ITSELF is merely a "medium" through which the "what" is projected. Jesus in fact tells us that your mind cannot exist without projecting, and it either projects ego or projects the Holy Spirit/truth.
So it's not really a question of whether you project or not, but more to do with "who with" or "what" you project. And that means that your perception isn't a matter of whether or not you are projecting, but what is coming out. And where does that something come from?
Well in fact he also tells us that the mechanisms for seeing begins by looking WITHIN first, at the content of your BELIEF, which you then project outward. So this tells you that in order to end up changing your perceptions you have to change your beliefs, so that you project a different belief, resulting in a changed perception.
But this too is not the end of the story. Because he in fact says that you believe IN what you VALUE, and so belief is something applied to what you value to try to give it value. And belief is also tied to what you WANT, because it then becomes what you want to SEE, resulting in you projecting it in order to end up perceiving it.
So in fact what you value or "hold true" or "make real" is what begins the whole process. What you value or hold true is what you want, which is what you then believe in, which is what you project, which is what you end up perceiving. This is the mechanism.
So while ACIM is seeming to tell you to shift your perceptions, or seems to be all about changing perceptions of things, it really isn't. That's an end result. It's main focus is that you find the cause in the mind, the root, the starting point of what ends up being projected and perceived. And that involves changing what you value and believe. And to do that you have to have a little willingness. Mainly because it all hinges around what you WANT, which is to do with your free will.
Ultimately then it's really an act of WILL, as to whether or not you will change your mind about what it values and believes is true. Which is why without a little willingness nothing can change at all. Will, or the attempted resistance of will, to become unwilling, is what made perception and the world in the first place, and it is through willingness that you return to freedom from it.
Perception just happens to be changed along the way as a side effect. It's not even something you can directly do anything about. Similarly to how you cannot directly "heal the body". You have to change the mind first. Just as Jesus says, the only meaningful change of mind is when you choose a totally different thought system, which really means choosing heaven over hell.
The only freedom you have left is the power of your decision, your choosing. "Mind is the mechanism of decision" and it is where the free will is. And you exercising your free will IS the only choice you have left in this world. So it all starts with your willingness and then your perception will automatically take care of itself as you adjust what you want and what you value.