As the form of fire, while it exists in the under-wood, is not seen, nor is its seed destroyed, but it has to be seized again and again by means of the stick and the under-wood, so it is in both cases, and the Self has to be seized in the body by means of the pranava (the syllable Om).

In plain words: Fire is hidden in wood. You cannot see it, but it is there, and you bring it out by rubbing sticks together again and again. In the same way, the Self is hidden in the body and is brought out by repeating the sacred sound Om.