阿彌陀經疏 1.238

1.238

經曰：「是諸人等皆得不退轉於阿耨多羅三藐三菩提」，次釋現獲益也。由念佛發願故，一即彼佛冥加，二即此佛潛衛，遂令求道之心不退、願生之志不移，故言不退轉。

The sūtra says: '...all these people attain non-retrogression from anuttarā samyaksaṃbodhi.' Next, this explains obtaining the benefit in the present. Because of remembering the Buddha and making vows, first, they receive the hidden aid of that Buddha; second, they receive the covert protection of this Buddha. Consequently, their mind seeking the path does not regress, and their aspiration wishing for birth does not waver; hence it says "non-retrogression" (avaivartika).