大般涅槃經義記 3.273

3.273

自下第三捨相入證，答上問中「云何作善，大仙今說」。彼問如何？釋有三義：一據修作問「凡夫二乘皆作善業不得菩提，菩薩云何修作善業能得菩提」，下佛教之，捨離有無，趣入中道，如是作善，便得菩提；二對果為問「若使當來有果可得，可須修善；若無可得，云何作善」，下佛答中明諸眾生現有佛性當必得果，如子在胎定生不久，但須修善；三對理為問「我今不知所趣入處，云何作善」，下佛答之，有如來藏可以趣入，宣修善業。

From here below is the third [section], relinquishing marks to enter realization, answering the question above: 'How should one perform good? May the Great Ṛṣi now explain.' What was that question? The explanation has three meanings: First, questioning based on cultivation: 'Ordinary beings and the two vehicles all perform good karma yet do not attain bodhi; how does a bodhisattva cultivate and perform good karma to be able to attain bodhi?' Below, the Buddha instructs them to abandon existence and non-existence and enter the Middle Way; performing good in this way, one immediately attains bodhi. Second, questioning in relation to the fruit: 'If in the future there is a fruit to be attained, one should cultivate good; if there is none to be attained, how should one perform good?' Below, in the Buddha's answer, he clarifies that all sentient beings presently have the buddha-nature and will definitely attain the fruit in the future, just as a child in the womb will definitely be born before long, so one only needs to cultivate good. Third, questioning in relation to principle: 'I do not know now the place to enter; how should I perform good?' Below, the Buddha answers that there is a tathāgatagarbha that can be entered, so one should cultivate good karma.