大毘盧遮那經供養次第法疏 1.34

1.34

「願令凡夫所住處」以下，第八奉請法身方便真言門，頌真言同前。法身恒住於本真，以恒住故令至法身，誦此真言直奉請，故云奉請方便法。

From "May the places where ordinary beings dwell" onward is the eighth, the mantra gate of the upāya of inviting the dharmakāya; the verses and mantra are the same as before. The dharmakāya constantly abides in original reality; because it constantly abides, it brings one to reach the dharmakāya. Reciting this mantra directly invites [it], and therefore it is called the method of the upāya of invitation.