He replied: "O Satyakâma, the syllable Om (AUM) is the highest and also the other Brahman; therefore he who knows it arrives by the same means at one of the two.

In plain words: Pippalada answers that Om stands for both the highest Brahman, which is beyond everything, and the lower form of Brahman that we can picture. So by meditating on Om, a person reaches one or the other.