"God Himself has established what you can project with perfect safety. Therefore, the Holy Spirit’s third lesson is: “Be vigilant ONLY for God and HIS Kingdom.”
This is a major step toward FUNDAMENTAL change. Yet it is still a lesson in thought REVERSAL, because it implies that there is something you must be vigilant AGAINST."
Ok so.... here is what ACIM boils down to. Anything regarding God's Kingdom, Heaven, Christ, The Sonship, Creation, is real and true and exists.
Anything else which is not part of that, is absolute bullshit and does not exist.
It is a black and white division. Only the truth is true. Only the creations of light are real. Spirit is in a state of grace forever. Heaven and Earth are opposite in every way. There is no world.
Ok so... anything relating to God and His Creation are real and true. Anything else is false. That includes the entire content of the separation idea, including this whole universe/world, Earth, all bodies, all of time and every event within time, every war, every death, every form of suffering and unhappiness, every suggestion that something has happened or gone wrong, it's all a lie and does not exist.
I know this is pretty extreme and black-and-white intense. But what Jesus is asking, is that we be vigilant ONLY for God's Kingdom. That means, we put all of our attention on God's Kingdom, we believe God's Kingdom is the truth, we live according to God's way of existing, we accept God's nature as the only truth, and we COMPLETELY IGNORE everything else that's coming from ego, recognizing it as utterly false, unreal, untrue and that it literally does not exist.
This means we really need to learn about God, about Heaven, about Creation, about Souls, about what the truth really is and what it is like and what it means and implies. So that we can live "only that". Jesus confirms He has been successful at doing this:
"There is nothing about me that you cannot attain. I have nothing that does not come from God. The difference between us now is that I have nothing else. This leaves me in a state which is only potential in you."
Notice that he says he has nothing that does not come from God. So he does not believe in there being any truth, reality, or existence, to anything that does not come from God. So that means, there is no body, no sickness, no death, no world, no separation, no sin, no guilt, no fear, no attack, no punishment, no war, no conflict, no loss, no lack, no forms, no physical objects, and nothing has happened. He is totally pure on this. 100% unwavering, vigilant only for God's Kingdom - what God has established as true. Everything else has been discarded and recognized for the lie that it is, and let go.
This means ultimately that we really need to learn to discern what is of God and what is not. What is God's nature and what is not. What is heaven like and what is it not like. What is true about us, permanently, and what is a temporary fiction.