Even though there are things in the world that change and are impermanent, the effect that the Dhamma can have on the mind when it’s used with precision is once and for all.
"Whatever attachments were causing suffering, whatever ignorance was causing the diseases of the mind — greed, anger, and delusion: That ignorance can be gone for good. That’s the good news of the Buddha’s teaching. Even though there are things in the world that change and are impermanent, the effect that the Dhamma can have on the mind when it’s used with precision is once and for all. The suffering can be gone for once and for all. So do your best to master this skill. Do your best to get the mind in position so that you can apply that skill with precision. When the Buddha talks about knowing for yourself, this is how he recommends you go about it. It’s not just a matter of sitting around and deciding that you like or dislike a particular teaching. It’s seeing where it’s properly applied. That’s when you really come to appreciate the power of the Dhamma." ~ Thanissaro Bhikkhu "Breath Meditation, Step by Step"