स्वयं प्रभुर्महात्मैव ब्रह्म ब्रह्मविदो विदुः ।अपरिज्ञातमज्ञानमज्ञानामिति कथ्यते
In plain words
Brahman -- itself the lord, the great self -- so the knowers of Brahman know it. What is not [fully] known is called ajñāna, for those who are in ignorance.