Allah mentions the blessing that He has bestowed upon His creation by subjugating these cattle for their use.
(so that they are their owners.) Qatadah said, "They are their masters." Meaning, He has made them subdue them. So they are submissive towards them and do not resist them; even if a young child comes to a camel he can make it kneel down, and if he wants to, he can make it stand up and can drive it, and it will meekly be led by him. Even if the train consists of a hundred or more camels, they could all be led by a young child.
(some of them they have for riding and some they eat.) means, some of them they ride on their journeys, and use them to carry their burdens to all regions.
(and some they eat.) means, if they want to, and they slaughter and sacrifice them.
(And they have (other) benefits from them,) means, from their wool, fur, and hair, furnishings and articles of convenience, comfort for a time.
(and (they get to) drink. ) means, their milk, and their urine for those who need it as medicine, and so on.
(Will they not then be grateful) means, `will they not worship the Creator and Subduer of that, without showing gratitude to others'