大般涅槃經集解 2.57

2.57

案僧亮曰：釋上已辦義也。僧宗曰：釋所以不生也。道慧記曰：釋心所以得自在，所作所以已辦也。

Sengliang states: This explains the meaning of "what was to be done" above.
Sengzong states: This explains why there is non-arising.
Daohui's Notes state: This explains why their minds had attained mastery and why what was to be done had been done.