In plain words
not recognizing this truth, incite [others] to say that the varṇas are human fabrications and that everyone is one and the same, taking outward forms as the basis and claiming that all human beings belong to one and the same race. It is indeed true! All human beings belong to one and the same race, but no one can deny that classes come about on the basis of guṇa and karma. These distinctions cannot be escaped. Not everyone in the world is sāttvic — only a few people are. That does not mean, however, that we can say all human beings are one and the same based on [outward] form. Sāttvic persons, rajasic persons, tamasic persons, and a mixed class — one cannot help saying so, is it not! It is precisely these that are called varṇas — so it has been said. Who denies this?
Among those commonly called Śūdras, purely predominant in tamoguṇa, how many are there not who are of pure sāttvic nature? Among the Brāhmaṇas, who are said to be purely sāttvic, how many are there not who are purely predominant in tamoguṇa? Hence the Bharatiya Vedic religion explains at great length the matter that the varṇas are determined not merely by [outward] form, nor merely by their births, but by [their] karma and guṇas.
The four varṇas are the various limbs of the one, single God. Whichever varṇa it may be, in its own place it is equally excellent. The aim of all the varṇas is precisely to serve Janārdana in the form of service to the people, through their respective dharmas.
There is some debate that Śūdras have no right to tapas, while a Brāhmaṇa has the right to tapas. Here is the matter we must principally note. 'Śūdra' does not refer to Śūdra birth; it refers to Śūdra-ness [the condition itself]. 'Brāhmaṇa' does not refer to Brāhmaṇa birth; it refers to Brāhmaṇa-ness. When it is said that the cow is not fit for riding, and that the horse is not fit for milking, that is not hatred of another's kind — it is said on the basis of differences of guṇa.