All sorts of worthless and filthy preoccupations come flowing into the mind at all times, turning it from something precious into a trash can. This is why we can’t find any marvels, any happiness in it at all. So to receive training in the Dhamma of the mind is something very important for this major factor within us. If the mind has Dhamma and reason within it, then whatever it displays in word and deed is correct and good and seldom ever falls off target. Whatever our actions, they’ll seldom fall off target. The heart will be happy and the body quite normal. If diseases arise in the body, they won’t cause any trouble that will have an effect on the mind or create any sort of mental illness within it. But when defilements fill the heart, they make it troubled and upset. If we simply complain about the effects without removing the causes, it won’t serve any purpose at all.
Venerable Ăcariya Mahà Boowa Ňàõasampanno, A Life of Inner Quality: A Comprehensive Guide to Buddhist Practice