大乘百法明門論開宗義決 1.151

1.151

平等正直無功用住等者。言平等者辯捨初位。由捨令心離沈掉等不平等性故。初證得心平等性。言正直者辯捨中位。又由捨故令平等心遠離加行自然相續。次後證得心平直性。無功用住者辯捨後位。復由捨故令正直心於諸雜染無所怯慮。最後證得無功用住性。具此三義簡三受中所有捨受故名行捨。

Regarding "abiding in equality, uprightness, and effortless application": "equality" explains the initial stage of equanimity. Because equanimity causes the mind to be separated from unequal states such as depression and agitation, one first realizes the equal nature of the mind. "Uprightness" explains the middle stage of equanimity. Further, because of equanimity, the equal mind is kept distant from exertion and continues naturally; next, one realizes the upright nature of the mind. "Abiding in effortless application" explains the later stage of equanimity. Further, because of equanimity, the upright mind has no dread or anxiety regarding defilements; lastly, one realizes the nature of abiding in effortless application. Possessing these three meanings distinguishes it from the feeling of equanimity among the three feelings; hence it is called formative equanimity.