Verse 7.17.1

यदा वै विजानात्यथ सत्यं वदति नाविजानन्सत्यं वदति विजानन्नेव सत्यं वदति विज्ञानं त्वेव विजिज्ञासितव्यमिति विज्ञानं भगवो विजिज्ञास इति ॥ ७.१७.१ ॥
॥ इति सप्तदशः खण्डः ॥

yadā vai vijānātyatha satyaṃ vadati nāvijānansatyaṃ vadati vijānanneva satyaṃ vadati vijñānaṃ tveva vijijñāsitavyamiti vijñānaṃ bhagavo vijijñāsa iti || 7.17.1 ||
|| iti saptadaśaḥ khaṇḍaḥ ||

1. Sanatkumāra said: ‘When a person knows for certain, then he can truly speak of the Truth. But without knowing well, he cannot speak of the Truth. One who knows for certain speaks of Truth. But one must seek knowledge in depth.’ Nārada said, ‘Sir, I seek knowledge in depth’.

Word-for-word explanation:

Yadā, when; vai vijānāti, a person knows well; atha, then; satyam vadati, he speaks what he knows to be the Truth; avijānan, without knowing it well; satyam na vadati, he does not speak of Truth; vijānan eva, knowing it well; satyam vadati, one can speak of Truth; vijñānam tu eva vijijñāsitavyam iti, but one must seek knowledge in depth; vijñānam bhagavaḥ vijijñāse iti, sir, I seek knowledge in depth. Iti saptadaśaḥ khaṇḍaḥ, here ends the seventeenth section.

Commentary:

Sanatkumāra says that when you know the Truth, whatever you say is nothing but the truth. You cannot say anything that is not the truth.

Truth is Truth, and there is no compromise in it. Once you know this Truth, everything else is irrelevant. But what if that Truth is associated with names and forms? Is that Truth? The scriptures admit it as a relative truth. It is not, however, the Absolute Truth.

The Absolute Truth is called ‘that’ because it is beyond the reach of the sense organs. As regards the relative truth, it is called ‘this’, because it is within the reach of the sense organs.

The Absolute Truth is difficult to understand. For instance, the elements in their pure form are beyond the reach of the sense organs, so they are sometimes referred to as ‘that’, but they are not the Absolute Truth. Brahman is the Absolute Truth.

In this connection it is to be remembered that fire was said to be red, water white, and earth black. Though it was said that the colours alone were real, this is not ‘real’ from the standpoint of Absolute Truth. These colours are also attributes. This is why the Absolute Truth is difficult to understand. Knowing the Absolute Truth is vijñāna.