Chanting Controls Mind
When the mind is finally trained to the point where it will think of nothing but Krsna, it will attain peace and will become very tranquil.
"The yogi whose mind is fixed on Me verily attains the highest happiness. By virtue of his identity with Brahman, he is liberated; his mind is peaceful, his passions are quieted, and he is freed from sin." (Bg. 6.27)
The mind is always concocting objects for happiness. I am always thinking, "This will make me happy," or "That will make me happy. Happiness is here. Happiness is there." In this way the mind is taking us anywhere and everywhere. It is as though we are riding on a chariot behind an unbridled horse. We have no power over where we are going but can only sit in horror and watch helplessly. As soon as the mind is engaged in the Krsna consciousness process specifically by chanting, then the wild horses of the mind will gradually come under our control.
(On the Way to Krsna)