Verily, he who purifies (Vâyu) is the sacrifice, for he (the air) moving along, purifies everything. Because moving along he purifies everything, therefore he is the sacrifice. Of that sacrifice there are two ways, by mind and by speech.

In plain words: The wind moves and cleans everything, so it is called the sacrifice, the sacred fire ritual. The ritual has two parts: one done with the mind and one done with words.