阿彌陀經疏 1.18

1.18

上來合有十四功德，無不超過三界六道，是故總名清淨世界。如論說言，莊嚴清淨功德成就者，偈言「觀彼世界相，勝過三界道」故。或有論說十八圓滿。今此經中依果清淨說此十五，若加後說正報四句，則有十九清淨功德。然經與論有同有異，於中委悉準之可知。

Altogether above there are fourteen virtues, none of which fails to transcend the three realms and six destinies; therefore, it is collectively called a 'pure world'. As the treatise says, regarding the fulfillment of the virtue of adorning purity, the verse states: / 'Contemplating the characteristics of that world, / It excels the ways of the three realms.' / Alternatively, some treatises speak of eighteen perfections. Now in this sūtra, fifteen of them are spoken of based on the purity of the dependent reward; if one adds the four clauses on the direct reward spoken of later, then there are nineteen pure virtues. However, the sūtra and treatise have agreements and differences, which may be understood by careful comparison.