How did the unmanifest Brahman become something that could be contemplated or understood by the mind?

According to the teachings in Chapter 50, Brahman, which is originally pure, formless, and beyond the senses, became qualified by Avidya, or ignorance. This process is what allowed it to attain expressibility and be given the name 'Sat' (Existence). Though it was originally beyond grasp, speech made it 'graspable by the intellect.' It was only after this that Brahman could enter the mind and take a conceptual form through the 'Omkar'. This Omkar-Brahman can then be the subject of meditation.