Speech yields the milk, which is the milk of speech itself to him who knows this Upanishad (secret doctrine) of the Sâmans in this wise. He becomes rich in food, and able to eat food,—yea, able to eat food.

In plain words: Whoever knows this secret teaching about the chants gets the full reward of speech, like milk from a cow. That person has plenty of food and the health to enjoy it.