That sacrifice is inclined towards the north (in the right way) in which there is a Brahman priest who knows this. And with regard to such a Brahman priest there is the following Gâthâ: 'Wherever it falls back, thither the man goes,'— viz. the Brahman only, as one of the Ritvig priests. 'He saves the Kurus as a mare' (viz. a Brahman priest who knows this, saves the sacrifice, the sacrificer, and all the other priests). Therefore let a man make him who knows this his Brahman priest, not one who does not know it, who does not know it.

In plain words: A ritual goes the right way when it has an overseeing priest who knows this. An old verse says such a priest goes wherever the ritual slips and protects everyone, like a mare protecting the riders. So people should choose a priest who truly knows this, not one who does not.