Verse 6.4.7

यद्वविज्ञातमिवाभूदित्येतासामेव देवतानांसमास इति तद्विदांचक्रुर्यथा तु खलु सोम्येमास्तिस्रो देवताः पुरुषं प्राप्य त्रिवृत्त्रिवृदेकैका भवति तन्मे विजानीहीति ॥ ६.४.७ ॥
॥ इति चतुर्थः खण्डः ॥

yadvavijñātamivābhūdityetāsāmeva devatānāṃsamāsa iti tadvidāṃcakruryathā tu khalu somyemāstisro devatāḥ puruṣaṃ prāpya trivṛttrivṛdekaikā bhavati tanme vijānīhīti || 6.4.7 ||
|| iti caturthaḥ khaṇḍaḥ ||

7. And whatever else was not properly known they understood was the combination of those three deities [fire, water, and earth]. O Somya, now learn from me how these three deities enter into a person and become threefold.

Word-for-word explanation:

Yat u avijñātam iva abhūt iti, and whatever they saw that was not properly known; samāsaḥ iti, the combination; etāsām eva devatānām, of these deities [fire, water, and earth]; tat vidāñcakruḥ, that they knew; somya, my son; yathā, as to how; imāḥ khalu nu, these very; tisraḥ devatāḥ, three deities; puruṣam, a living being; prāpya, entering [as food]; trivṛt trivṛt ekaikā bhavati, each one becomes threefold; tat me vijānīhi iti, learn that from me. Iti caturthaḥ khaṇḍaḥ, here ends the fourth section.

Commentary:

Previously the scholars did not know these deities—the three elements—separately. They began to understand better when they saw the elements working in living beings.