We have to break the world into bits with our perception, and I begin to suspect that this has a lot to do with our mission to inject love into everything in our surroundings. If we couldn't separate things off (like the color red), we couldn't give them names, and then how could we come to love them?
What we so separate, we recombine with our thinking into larger entities, and name them too. So: dense, soft, malleable, yellow, found in nuggets, we combine into a larger entity, and call it the metal gold. If I weren't able to recombine a million fragmentary percepts into one entity, I wouldn't even have a self, a self separate from all the other things. So it's kind of a paradox, that only through this unifying, recombining thinking can I define myself as separate, me against the world.
But that's only because thinking gets stopped in its reuniting of all things, before it can reunite me with something else. What stops it? Percepts,( or mental pictures?) giving me my inside and my outside. If I take the brakes off even for an instant, thinking starts reuniting me with all kinds of others -- family, country, humanity, living things, existing things -- it never stops. It's universal, that's why! And yet I can always brake again at any point along the way and find an "inside" and an "outside." As an American, my outside is everyone who isn't, and my inside is everyone who is.
Thinking holds no allegiance to limits, but we have to hold it back so we can look at things and learn about them.
When I think of "triangle", what keeps my ever-expanding thinking from passing straight through to "all geometrical figures" and beyond? I hold it back with my mental picture of "triangle." This is, more or less, a black triangle on a white background, equilateral, resting on its base. Another person might picture a chalk triangle on a blackboard. A blind person might have one made of cold steel. All these individual mental pictures we use, to keep our thinking from going too far and reuniting everything at once. We extract one concept from the unified world of concepts so we can look at it and give it a name.
If two friends thinking "triangle" can make a triangle, then I'm one angle of the base, my friend's the other angle of the base, and the concept is the tip. Thinking wants to fly up and away, but we hold it down, with me leaning one way and my friend the other. We hold it down with our mental pictures, and our wills, but what we hold down is a little piece of heaven. In this way, we keep heaven down here on earth.