大般涅槃經義記 6.314

6.314

In the Tathāgata's promising to make his mind resolute, the Buddha first addresses the assembly: "King Ajātaśatru has doubts; I shall make his mind resolute." What does this mean? King Ajātaśatru just now heard the two statements on the road and immediately gave rise to doubts, not knowing whether the Tathāgata would be willing to rescue him and make him like Sunakkhatta, or whether he would not rescue him and let him be like Virūḍhaka, Kokālika, and the others, falling into the Avīci hell. Judging from his subsequent meeting with the Buddha, where his doubts are removed and he attains certainty, his doubtful intention was precisely this. The Buddha below accepts the task and causes him to know that the Buddha definitely intends to rescue him, which is called "making his mind resolute."