If we look deep enough within ourselves there seems to be an absolute continuity which abides in all sentient beings despite their differences from each other, including death (yes, this continuity surpasses death). There are many names for it such as soul, One Mind, pure Mind, Buddha-nature, ātman, Spirit, or God (theos) or Christ.
That we cannot conceive of this continuity with thought or by conceptualizing it, is to be expected according to the great mystics like Siddhartha. Still, we try to do it which turns into religion, philosophy and metaphysics. Here, we are using thought as an equivalent of the unthinkable and inconceivable.
Thought is useful for our imagination which can be used to make a virtual world (ancient Rome, Paris, London or St. Petersburg are good examples) which we fall prey to in the sense of attaching to this architecture when there is nothing fundamentally real to attach to.
Ultimate reality is always found in this continuity although very few get that far so as to have direct knowledge of it. Everything else is an appearance which is transitory, which is the snare of suffering, and is not real. But we are already entangled in this snare during rebirth. Joy is short-lived while suffering is long-term.
Religions like Buddhism and Christianity offer mankind an escape from the world of appearance. But this escape usually becomes only hope which is just another kind of appearance (even secular progress rests upon hope).
If there is any kind of escape it has to be direct intuition or gnosis of ultimate reality hidden in this continuity which entails a process of negation of all appearance including thought, upon which our human world is based. And since there is nothing higher than ultimate reality there is no way to see it except to merge with it, completely. This mergence, the noun, is absolute knowing but nontransferable (mergence cannot be transferred by teacher to student).