大般涅槃經義記 6.156

6.156

後三一對，前二因圓，後一果極。就前二中，初一解圓，後一行圓。正遍知者多義如下，當相論之，理無偏邪故名為正，於理窮照說為遍知。「明行足」者多義如下，明是證行，行是教行，證心清淨離闇稱明，曠集諸善說之為行，此二圓滿名明行足。言「善逝」者多義如下，當相論之，善者名好，逝之言去，如來好去故云善逝。如來德滿，更何處去？如言好去，雖無去處，非不能去。如劫盡火，雖無所燒，非不能燒，此亦如是。

The latter three form a pair: the first two are the perfection of the cause, and the latter one is the culmination of the fruition. Among the first two, the initial one is the perfection of understanding, and the latter is the perfection of practice. 'Samyaksambuddha' (Correctly and Fully Enlightened One) has multiple meanings as below; discussing it in terms of its characteristics, principle has nothing biased or crooked, hence it is called 'correct'; fully illuminating principle is spoken of as 'universal knowledge'. 'Vidyācaraṇasampanna' (One Perfect in Knowledge and Conduct) has multiple meanings as below: knowledge is the practice of realization, and conduct is the practice of teaching; the realization-mind being pure and free from darkness is called 'knowledge', and extensively gathering all wholesome [deeds] is spoken of as 'conduct'; the completion of these two is called 'perfect in knowledge and conduct'. As for 'Sugata' (Well Gone), it has multiple meanings as below; discussing it in terms of its characteristics, 'su' means good, and 'gata' means gone; the Tathāgata has gone well, hence he is called 'Sugata'. The Tathāgata's virtues are complete, so where else would he go? As it is said, he has gone well: although there is no place to go, it is not that he cannot go. It is like the fire at the end of an aeon: although there is nothing to burn, it is not that it cannot burn; this is also like that.