大毘盧遮那成佛經疏 4.45

4.45

The verse says: 'Born of a pure clan', which means born in the family of one of the four great varnas such as brāhmaṇa. If one is a caṇḍāla or the like, because their family traditions inherit and practice impure deeds, their lineage is mostly degraded and evil. If one performs the dharma-transmission abhiṣeka for such a person to have him propagate the great Dharma, it would cause others to feel contempt, or become a cause and condition for the decline of the Dharma. It is just as when a bhikṣu receives full ordination, those from extremely low clans that would disgrace the saṃgha are also screened out. If one merely forms a karmic connection to receive the dharma, then that is not under discussion. Furthermore, if from long ago one has had the cause and condition of arousing bodhicitta, that is to be born in the Tathāgata's clan, which is the most supreme family.