法華義疏 2.408

2.408

「號曰淨身」者，累無不盡為淨，德無不圓稱身，廣說十號則舉此土之名，略說三號即存彼國之稱。如來為人，應供為斷，正遍知為智。人具智斷在義略圓，故但三也。

As for "named Pure Body": there is no defilement that is not exhausted, which is "pure"; there is no virtue that is not perfected, which is called "body." Expounding the ten titles at length cites the names of this land; stating the three titles briefly preserves the appellations of that country. The Tathāgata corresponds to the person; Arhat corresponds to severance; Samyaksaṃbuddha corresponds to wisdom. When the person is endowed with wisdom and severance, the meaning is briefly perfected; hence there are only three.