In plain words
What is it that is glad at seeing food, delighted at seeing beauty, carried away at seeing a fragrance: the senses, the body, or the Ātma? It is not the body; still less is it the senses. The root principle that listens to all, rules all and cherishes all, that governs the world, is the principle of the Ātma. It is the root of the outer world. It is the source of the inner world. Only when we keep this principle of the Ātma as our goal will the sway of the body and senses, which are impermanent, transient and Asatya, have no hold over us in any way. Of all the senses, the most important is the tongue. If we bring this one under control, all the senses too come easily under our control. In the Kaṭha Upaniṣad they compared these senses to horses. Take the horse here as the example, and we understand the close bond between the tongue and the horse. There may be a horse that runs well, sturdy and swift. But even a horse that runs at such speed, when we set a small piece of iron in its mouth as a bit and draw it tight, comes under our control, its whole body with it. How this small bit can check a horse that runs so strong and so fast! For the horse, it is the mouth that matters most. When that is checked, the whole horse comes under control. For this horse of the five senses, it is the mouth that matters most. With one small rudder we can keep the boat safe, however great the storm that comes. From one small spark we can make a fire as big as we please. Speech is just like a spark of fire. We can make every kind of effort to bring this spark under control. If we master speech, we become those who have mastered the world itself. By this speech we can do deeds however great. We can do deeds however base. This very speech brings blessing. It brings abuse. So Jayadeva went on praising this tongue:
O tongue, knower of tastes, you who love what is sweet, I tell you what is true and good, the highest: … the sweet syllables, Govinda, Dāmodara, Mādhava.
O tongue that knows taste! O sacred tongue! Tongue that speaks gentle, sweet words! Do not run into needless words; do the remembrance of the Name, sweet, that gives the deepest Ānanda: so he went on praising it.