This is a pretty deep and abstract passage from lesson 167, "There is one life and that I share with God." It speaks of how immortal mind is permanently awake, it thinks of being asleep in which it dreams of a world of spacetime, everything in that dream is nothing with no consequences (there is no world) because it’s a dream of NOT existing and NOTHING happening, and then it simply awakens, the dream world disappears, and it resumes creation with God. You have to read it slowly to really get a feel for it. So I added some commentary...
"The mind (shared with God in heaven) can ***think*** it sleeps, but that is all (has a THOUGHT of sleeping - tiny mad idea). It cannot change what is its waking state (can’t change the truth). It cannot make a body, nor abide within a body (cannot make a REAL body). What is alien to the mind does not exist because it has no source. For mind creates all things that are (all creations in heaven), and cannot give them attributes it lacks, nor change its own eternal, mindful state. It cannot make the physical (literally impossible to REALLY create the physical). What seems to die (the illusion of the physical) is but the sign of mind asleep (mind can only imagine physicality, it cannot create it as a permanent creation, and we are currently "living" within that IDEA).
The opposite of (eternal) life can only be another ***form*** of life (a real opposite is impossible, the physical is not completely opposite, it’s still within God - safe in God, dreaming of exile). As such, it can be reconciled with what created it, because it is not opposite in truth. Its form may change; it may appear to be what it is not. Yet mind is mind (mind is still mind even if it experiences wakefulness or THINKS OF a sleeping state) awake or sleeping. It is not its opposite in anything created (mind MAKES the illusion that mind is absent, free will is used to make the illusion of imprisonment), nor in what it seems to make when it believes it sleeps (even death is a deliberately chosen idea by a *living* mind).
God creates only mind awake. He does not sleep, and His creations cannot share what He gives not, nor make conditions which He does not share with them (not possible to make an actual separation, death, body, etc) The **thought** of death is not the opposite to thoughts of life (absolute death is not possible at all, the thought of death is just an idea WITHIN the awake mind and are illusions, love has no opposite, so death is not a true opposite, it’s just a state of thought). Forever unopposed by opposites of any kind, the Thoughts of God (souls etc) remain forever changeless, with the power to extend forever changelessly but yet within Themselves, for They are everywhere.
What seems to be the opposite of life (eternal life) is merely sleeping. When the mind elects to be what it is not (e.g. trying to be a world or body), and to assume an alien power which it does not have (made-up ego laws or ability to really sin), a foreign state it cannot enter (illusions of vulnerability, sickness, suffering, death), or a false condition not within its Source (nightmares, attack, sickness etc), it merely ***seems*** to go to sleep a while. It ***dreams*** (thinks of) of time (this whole universe); an interval in which what *seems* to happen never has occurred (tiny tick of time, nothing in this world ever happened), the changes wrought are substance-less (no real consequences, no sin), and all events are nowhere (nothing ever really happens because its a thought of "nothing happening"). When the mind awakes (to the Kingdom of God, and stops dreaming up a world), it but continues as it always was (in heaven).
Let us today be children of the truth, and not deny our holy heritage. Our life is not as we imagine it. Who changes life because he shuts his eyes (failure to acknowledge reality, denial of God), or makes himself what he is not (trying to be a dead body) because he sleeps and sees in dreams (this world) an opposite to what he is? (Everything you see in this world is OPPOSITE to reality - "Earth, heaven’s opposite in every way.") We will not ask for death (this world - "without the idea of death tehre is no world") in **any form** today. Nor will we let imagined (bodies, planets) opposites to (eternal) life abide even an instant where the Thought of Life Eternal has been set by God Himself.
His holy home (heaven) we strive to keep today as He established it, and wills it be forever and forever. He is Lord of what we think today. And in His Thoughts, Which have no opposite, we understand there is one life (eternal life with God), and that we share with Him, with all creation (the Kingdom of God, not this world), with their thoughts as well, whom He created in a Unity of life (all created beings in heaven) that cannot separate in death and leave the Source of Life (God) from where it came.
We share life because we have one Source (God), a Source from Which perfection comes to us, remaining always in the ***holy minds*** which He created perfect (yes God DID create many minds!). As we were, so are we now and will forever be ("we" existing within reality). A sleeping mind must waken (individually) as it sees its own perfection mirroring the Lord of Life so perfectly it fades into what is reflected there (sees the real world, reflects holiness here). And now it is no more a mere reflection (when you go to heaven). It becomes the thing reflected, and the light which makes reflection possible. No vision now is needed (vision/perception has no purpose IN heaven/reality - "Indeed, you cannot remain in the world with this knowledge."). For the wakened mind (awake in heaven, not in a body or in this world any more, not in the dream, not having dreams, not having the thought of the world, not asleep, fully awake in God) is one that knows its Source, its Self, its Holiness."