The world is acted upon by way of the mind
And all good things and bad
Exist in the world by way of the mind.
It would be easy to interpret this verse from the Samyutta Nikaya as philosophically idealistic as several schools of buddhism have done, and go as far as saying that the world is simply a projection of the mind. However, it seems that the buddha, like Patanjali, thought there there was indeed a world that exists independently of the mind. However, it also seems that this verse can be seen to be asserting -- somewhat phenomenologically -- that all we can know of the world comes via our sensorium: the perceptions we experience via our senses.
The world is apprehended by way of the mind.
One meaning of this word, "apprehended" is to "catch, capture" or "seize" while the secondary meaning is to "appreciate, recognize, discern, perceive, realize, grasp, understand" and "comprehend." I would argue that while the secondary meaning is most appropriate to this reading, in that we come to recognize, perceive and understand the world via the mind, it is also true that we may "seize" upon our perceptions -- often to our detriment. But it is clear: it is through the way of the mind that we come to perceive and understand the world.
The world is acted upon by way of the mind.
If you stop and take a moment while reading this, to look around at your surroundings, you'll see that everything, from the computer you are reading this through (not to mention the internet itself) to the table you are sitting at and the chair you are sitting on originated in the mind of someone who had a vision or inspiration and then made an effort to make it visible and physical. This is simply another way of pointing out that action follows the mind -- whether with conscious volition or unconscious conditioned reactivity, all action is preceded by mental formations.
Exist in the world by way of the mind.
And with this sentence there can easily be a more idealistic interpretation to the extent that to an often very great degree it is the mind itself that projects "good" and "bad" upon the world. For instance, two people step out onto their porch on a rainy day. For the farmer who had been praying for rain, it is a good day! For the parent who had promised their child a picnic, it's a bad day. Perception is all that determines the "good" and "bad" of it.
BUT, it would be a form of spiritual sickness to take this to the extreme we see often voiced by so-called 'non-dual' practitioners who assert "it's all good" or that "good" and "bad" are always a mental projection. This is getting caught in the 'absolute' while denying the 'relative.' In this world of multiplicity, there is good and bad.
However, when we look at much of the cancers that eat away at our society such as racism, sexism, homophobia, classist exploitation, and bigotry of all kinds, along with the headlong rush into climate catastrophe, we are foolish to ignore that these are "bad" in that they cause much societal and individual suffering. But it is also true, in the spirit of this sentence and verse, that such systemic ills do indeed arise by way of the mind. By way of greed, hatred and ignorance.
For instance, at the time of the buddha (and for many fundamentalist Hindus today) the caste system is accepted as being simply part of the "natural order" of the cosmos. The buddha saw the suffering of such a system and rejected its validity and justification by pointing out that not all cultures had such a system, and therefore the caste system is a cultural creation (a creation that arose via the mind).
Mindfulness meditation offers us the all-too-rare opportunity to see the nature of mind; it's functions and abilities. Mindfulness meditation practiced to its fullness can be a form of metacognition leading to greater clarity regarding the nature of the mind. We can, through practice, change our relation to the mind and use the mind towards the betterment of all life.