首楞嚴義疏注經 1.99

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十德具足，三品居財，故云長者居士。又守道自怡，寡欲蘊德，故曰居士。佛為化主，王請須臨，臣為輔佐，餘聖可赴。

Possessing the ten virtues and occupying three ranks of wealth, they are called "elders and householders" (śreṣṭhin and gṛhapati). Also, preserving the Way in self-contentment, having few desires, and storing up virtue, they are called "householders." The Buddha is the leader of conversion, so the king's request had to be attended by him; the ministers were assistants, so the remaining noble ones could attend them.