द्वे वाव ब्रह्मणो रूपे मूर्तं चामूर्तं चाथ यन्मूर्तं तदसत्यं यदमूर्तं तत्सत्यं तद्ब्रह्म यद्ब्रह्म तज्ज्योतिर्यज्ज्योतिः स आदित्यः स वा एष ओमित्येतदात्मा स त्रेधात्मानं व्यकुरुत ओमिति तिस्रो मात्रा एताभिः सर्वमिदमोतं प्रोतं चैवास्मिन्नित्येवं ह्याहैतद्वा आदित्य ओमित्येवं ध्यायंस्तथात्मानं युञ्जीतेति ॥५.३ ॥
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. What is Brahman is light, and what is light is the sun. And that indeed 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 himself to the Self."