द्वे वाव ब्रह्मणो रूपे मूर्तं चामूर्तं च ।अथ यन्मूर्तं तदसत्यम् यदमूर्तं तत्सत्यम् तद्ब्रह्म तज्ज्योतिः यज्ज्योतिः स आदित्यः स वा एष ओमित्येतदात्माभवत् स त्रेधात्मानं व्याकुरुत ओमिति तिस्रो मात्रा एताभिः सर्वमिदमोतं प्रोतं चैवास्मीति एवं ह्याहैतद्वा आदित्य ओमित्येवं ध्यायत आत्मानं युञ्जीतेति ॥६.३ ॥
In plain words
There are two forms of Brahman: the formed and the formless. What is formed is unreal; what is formless is real, and that is Brahman, and that is light. What is light is the sun; and that became the self of this Om. He divided himself in three: Om has three measures, and by them all this is woven, warp and woof, upon him. So it is said: "Meditating thus, that the sun is Om, let a man yoke his self."