§70. "Now what is worldly equanimity? There are these five strands of sensuality. Which five? Forms cognizable via the eye — agreeable, pleasing, charming, endearing, fostering desire, enticing; sounds cognizable via the ear... aromas cognizable via the nose... flavors cognizable via the tongue... tactile sensations cognizable via the body — agreeable, pleasing, charming, endearing, fostering desire, enticing. Any equanimity arising in connection with these five strands of sensuality is called worldly equanimity.
And what is unworldly equanimity? There is the case where, with the abandoning of pleasure & pain — as with the earlier disappearance of elation & distress — one enters & remains in the fourth jhana: purity of equanimity & mindfulness, neither pleasure nor pain. This is called unworldly equanimity.
And what is an even more unworldly unworldly equanimity? Any equanimity that arises in one free from (mental) fermentation while he/she is reflecting on his/her mind that is released from greed, released from aversion, released from delusion: this is called an even more unworldly unworldly equanimity."
— SN 36.31
§71. "There is equanimity coming from multiplicity, dependent on multiplicity; and there is equanimity coming from singleness, dependent on singleness.
"And what is equanimity coming from multiplicity, dependent on multiplicity? There is equanimity with regard to forms, equanimity with regard to sounds... smells... tastes... tactile sensations [& ideas: this word appears in one of the recensions]. This is equanimity coming from multiplicity, dependent on multiplicity.
"And what is equanimity coming from singleness, dependent on singleness? There is equanimity dependent on the sphere of the infinitude of space, equanimity dependent on the sphere of the infinitude of consciousness... dependent on the sphere of nothingness... dependent on the sphere of neither perception nor non-perception. This is equanimity coming from singleness, dependent on singleness.
"By depending & relying on equanimity coming from singleness, dependent on singleness, abandon & transcend equanimity coming from multiplicity, dependent on multiplicity. Such is its abandoning, such its transcending.
"By depending & relying on non-fashioning, abandon & transcend the equanimity coming from singleness, dependent on singleness. Such is its abandoning, such its transcending."
— MN 137
§72. To purify the heart, we have to disentangle our attachments to self, to the body, to mental phenomena, and to all the objects that come passing in through the senses. Keep the mind intent on concentration. Keep it one at all times. Don't let it become two, three, four, five, etc., because once you've made the mind one, it's easy to make it zero. Simply cut off the little 'head' and pull the two ends together. But if you let the mind become many, it's a long, difficult job to make it zero.
And another thing: If you put the zero after other numbers, they become ten, twenty, thirty, forty, fifty, hundreds, thousands, on to infinity. But if you put the zero's first, even if you have ten thousand of them, they don't count. So it is with the heart: Once we've turned it from one to zero and put the zero first, then other people can praise or criticize us as they like but it won't count. Good doesn't count, bad doesn't count. This is something that can't be written, can't be read, that we can understand only for ourselves.
— Ajaan Lee (Inner Strength)