In plain words
Satyaṃ brūyāt priyaṃ brūyāt na brūyāt satyam apriyam. That is, we must not speak untruth because it is pleasing. Nor must we speak Satya harshly just because it is unpleasant. Every human being must speak Satya alone. We must speak Satya that is pleasing. This is what the Bhagavad Gītā says: Anudvegakaraṃ vākyaṃ prīti hitaṃ ca yat; speech must be beneficial and pleasing, free of agitation, and pleasing. When we see a person who has no eyes, truly he has no eyes; that much is Satya. When, because it is true, we call him, "O blind man!", it feels unpleasant to him. The moment he hears that word, he is hurt. What was spoken is Satya. It caused the person displeasure. When we see a lame man, we know the truth that he has no legs, but when we call him, "O lame man!", his mind is hurt. Even though it is true, it is far better to take a way that does not hurt him and call him in some other way. Saying, "Satya is Satya", we must not bring in a Satya that hurts others. When man's conduct is not proper, man loses his very individuality. So, if we wish to develop the individuality of our humanness, we must follow the path of Satya and the path of what is pleasing.
The Upaniṣad is like the head of all the Vedas. Among these Upaniṣads, the Īśāvāsya Upaniṣad has risen to the place of the head. The Īśāvāsya Upaniṣad is in the Yajurveda, in the Śukla Veda, in the form of mantras. Based on the path of karma, it went on teaching up to the thirty-ninth chapter. By the time it enters the fortieth chapter, it begins Jñāna. From that very point the Īśāvāsya Upaniṣad begins. That which sets forth karma is Jñāna. The basis of Jñāna is karma. That which brings karma and Jñāna into harmony is the Upaniṣad. So man must, without fail, do the karmas he has to do. We must perform good, good karmas with a good mind. We must give no room to the sense of possession that says, "I alone must enjoy the fruit of this karma." We must give no room to the Ahaṅkāra that says, "It is only because I did it that I could gain the fruit of this karma." This Ahaṅkāra and this sense of possession make man bound by karma. In this Īśāvāsya Upaniṣad it went on teaching: whatever enjoyment man has to enjoy, enjoy it through sacrifice.