無量壽經優婆提舍願生偈註 2.117

2.117

應知者，應知此三種莊嚴成就，由本四十八願等清淨願心之所莊嚴。因淨故果淨，非無因、他因有也。

'One should know' means that one should know that these three kinds of adorned perfections are adorned by the pure vow-mind of the original forty-eight vows and the like. Because the cause is pure, the result is pure; they do not arise without a cause or from another cause.