I've recently come to appreciate what these two terms mean. When I am taking over control, doing everything myself, identifying what things are and what they mean, assigning labels and projecting judgements, I am actually "narrowing down".
I narrow because I am actually tying to narrow what things are. To put them in boxes. Interestingly I can't just freely use my mind to narrow things down without making my mind narrow down as well. Any attempt to label the specific forces my mind to exclude.
When doing this a lot, I couldn't help but notice that my intellectual pursuits felt like they were keeping me stuck in a box. I kept feeling small and childish and afraid. The more I seemed to become close to finding out what the truth was about something specific, the narrower my outlook became and the more I felt hemmed in.
When I confine something to being something specific, focusing on its form and so on, I become blinded by that perception of form. I might think I'm being objective or open but it's not possible to focus on the specific without making your mind become specific.
You might have thought for a long time that you can just use your mind and your thinking however you please, as if the way you think about stuff has no effect on you. But it totally does.
When you're in the business of trying to give meaning to everything and to interpret and judge everything "alone", that aloneness is isolating and actually inhibits your awareness. It closes you down.
Also interestingly the more you "home in on" what you think something is or means, isolating it into a nice tidy definition, you'll think you are "opening up" to the truth, when in fact you are closing yourself off from the truth.
You'll also find that the more you obsess over trying to find the perfect explanation or cause for something highly specific, the more it will slip through your fingers. And you'll be driven mad with the exasperating endless search for answers that can never be satisfies - as you seek and do not find.
Things in the world become true in your mind only when you start splitting the world into separate pieces and putting labels on them. Trying to categorize them into various boxes. This obsession with dividing things up to try to make sense of them or to get a better understanding of them, masquerades as becoming open to what they are. But it's doing exactly the opposite.
If to "narrow down" or pin down what something is, or means, causes your mind to actually close, then doing the opposite opens your mind. To become open-minded doesn't just mean you're not very attached to some things and willing to entertain alternatives, it means you are not in the business of being closed.
To be open minded is to stop narrowing everything down on your own. To be open minded is to be willing to receive the Holy Spirit and allow him to see and decide and judge for you. You're open to his judgement because you're refusing to confine yourself within narrow separating judgements.
The very walls you put around the things you see become blocks to awareness in your perception. As you label and section things off your mind goes into those boxes along with the things you put in them. As you imprison, as you isolate things to form and physicality, your mind shuts down and becomes small, just like those objects.
To become open minded we have to be actually willing to let go of judging and let go of labeling and let go of giving meaning to things. What the Holy Spirit wants for us is to share his perception of wholeness. "The perceptual contents of miracles is wholeness."
This also requires transcending separations between objects by not focusing so much on their differences and exclusive qualities. This is what the ACIM workbook has you doing, overlooking and being non-specific in your selection of objects to consider around you, so that you move towards a more abstract or generalized viewpoint.
That means seeing from a whole perspective, looking with wholeness (holiness), seeing wholeness, and giving a single meaning to everything. It is far more abstract and open rather than being narrow and specific. You have to be "open to everything" (to the single whole) in order to be open minded.
The Holy Spirit doesn't attempt to "understand" the world, in terms of breaking it up into specific things in an attempt to analyze and judge its parts. To figure out the inner workings or relationships between separate objects. He knows that such an analysis leads to separating, partial, blind perspectives, which cannot grasp the whole.
The more you narrow things down in the search for explaining what is true of it, the more out of touch you become with the big picture. The big picture, the real truth, is not narrow at all. It is expansive and abstract and unlimited.
You have to be in an unlimited state in order to really see from a perspective of wholeness, to be able to discern what anything really is. Unless you can see everything at once, you cannot really be in a position to judge correctly.
Open mindedness is a willingness to surrender the position of trying to be God, or trying to fulfill the Holy Spirit's function. It's a willingness to recognize you cannot judge or accurately discern the meaning of anything on your own, and your own exclusive learning has mislead you down dark paths that have only made you suffer.
To be closed-minded has in fact shut you off from happiness and from health. It has caused you to draw conclusions which are narrow and limiting and which take sides. Partitioning off aspects of your awareness and labeling and judging them as right or wrong, and pitting them against each other. Dividing up your "world" into a fragmented experience, erecting walls and inducing darkness.
Openness is really the absence of walls, and it is this absence of obstructions or "obstacles to peace" that allows light to shine and extend. To be enlightened is to be open minded, in which the mind becomes aware of the whole of reality at once. It can't do that if it's constantly focusing on trying to split everything apart and give it a name.
To "not know" what things are, or more to the point to not understand what the world is, is to recognize that on the whole it is fundamentally insane and does not make sense. Trying to make sense of an illusion is like trying to keep its illusory nature and study it. Or to study the ego. It is better to let it be what it is and move into a space of awareness, of not needing to know because the Holy Spirit can know for you.
The Holy Spirit is more than just a guide in this sense. We could say that he is the gate of heaven. That which connects your mind to both worlds, while two seem to persist, until you can accept oneness and singularity again. From his perspective, the entire world has a single meaning. "In this shared purpose is one meaning shared by everyone and everything you see. You do not have to judge, for you have learned one meaning has been GIVEN everything, and you are GLAD to see it everywhere."
"Learning is useless in the Presence of your Creator, Whose ACKNOWLEDGMENT of you, AND YOURS OF HIM, so FAR transcends ALL learning, that EVERYTHING you learned is meaningless, replaced forever by the knowledge of love and its One meaning."
"There is NO confusion in the Kingdom, because there IS only one meaning."
"This is the light which shows no opposites, and vision, being healed, has power to heal. This is the light which brings your peace of mind to other minds, to share it and be glad that they are one with you and with themselves. This is the light which heals because it brings single perception, based upon one frame of reference from which one meaning comes."
"You cannot see alone. Sharing perception with Him Whom God has given you, teaches you how to RECOGNIZE what you see. It is the recognition that NOTHING you see means ANYTHING alone. Seeing WITH Him will SHOW you that all meaning, INCLUDING YOURS, comes not from double vision, but from the gentle fusing of everything into one meaning, one emotion and one purpose."