The wise know that the Pranava (Om) is the new form, for it creates. The Pranava is said to be of two kinds: subtle and gross, distinguished by their forms.
सूक्ष्ममेकाक्षरं विद्यात्स्थूलं पंचाक्षरं विदुः । सूक्ष्ममव्यक्तपंचार्णं सुव्यक्तार्णं तथेतरत् ९ ।
The subtle one is of a single syllable where the constituent five syllables are not differentiated clearly. The gross one is of five syllables where all the constituent syllables are manifest.
जीवन्मुक्तस्य सूक्ष्मं हि सर्वसारं हि तस्य हि । मंत्रेणार्थानुसंधानं स्वदेहविलयावधि 1.17.१० ।
The subtle one is for the liberated living soul (jīvanmukta). The need for the contemplation of the meaning through the mantra is only upto the destruction of the physical body.