In this sutta the Buddha declares that all human beings are equally capable of reaching the highest stage of spiritual perfection. Here he explicitly denounce the brahminical idea that those belonging to the “lowest” strata of indian society were less endowed with spiritual capacity.
“Whether khatthiya[i], brahmin[ii], vessa[iii], sudda, candala[iv] or scavenger, if one is energetic and resolute, always firm in exertion, one attains the supreme purity: know, O brahmin, that this is so”.
Suddhikasuttaṃ, Brāhmaṇasamyutta, Sagāthāvagga, Saṃyutta Nikāya.