大毘盧遮那成佛經疏 5.12

5.12

The first line says: 'Child of the Buddha, listen attentively.' In Sanskrit, kula means family or clan, and putra means son. If explained according to conventional truth, being born among the four castes is in all cases called a great family; hence they are called 'sons of good family' (kulaputra). Now, being able to be born into the house of the Tathāgata, it is the most supreme among all families; hence they are called 'sons of good family'. The ācārya said: 'It is appropriate to grasp the sense and say "child of the Buddha", which makes the meaning prominent.'