anudvekaram vaakyam satyam priyahitam cha yat |
svaadhyaayaabhyasanam chaiva vaangmayam tapa ucchyate || 15 ||

Those words that do not perturb others, that are true, pleasant and beneficial, and also the practice of recitation of scriptures, that is called the penance of speech.
anudvekaram : do not disturb others
vaakyam : words
satyam : true
priyahitam : pleasant and beneficial
cha : and
yat : those which
svaadhyaaya : recitation of scriptures
abhyasanam : practice
cha : and
eva : also
vaangmayam : speech
tapaha : penance
ucchyate : is called
Having described the penance of the body, Shri Krishna now describes penance of the mind, mental austerity or vaangmaya tapa. He mentions four conditions of speech : that it should be true, it should be pleasant to hear, it should benefit the other person, and it should not cause any disturbance in the other person’s mind. Whenever we speak statements that fulfill all these four conditions, we are practicing penance of the mind. Putting it differently, we are not wasting or dissipating the energy of our speech when we speak like this.
Initially, we may think that satisfying even two or three of these conditions is impractical. However, speaking tactfully is a skill needed in our daily lives. For instance, what is true may not always be the most pleasant thing to convey. In the office, we have to deliver all kinds of messages to people without them losing face. Even in the home, while talking to spouse, just conveying information factually does not always work best. Therefore, putting thought into choosing our words carefully has practical as well as spiritual benefits.
Now, many of us have an urge to say something when we are by ourselves. Here, Shri Krishna suggests that we recite scriptures daily, like chanting the second chapter of the Gita, for instance. Doing so satisfies our urge of speaking, and also forces the mind to contemplate the Gita teaching rather than stray here and there. In fact, it becomes a form of meditation as well. Once we memorize the shlokas, we can contemplate upon them whenever we want, without having to rely on a book.