Answer: Nichiren Daishonin teaches:
"At the time of his extinction, the World-Honored One of Great Enlightenment lamented, 'Now I am about to enter nirvana. The only thing that worries me is King Ajatashatru.' Bodhisattva Kashyapa then asked him, 'Since the Buddha’s mercy is impartial, your regret in dying should stem from compassion for all living beings. Why do you single out only King Ajatashatru?' The Buddha replied, 'Suppose that a couple has seven children, one of whom falls ill. Though the parents love all their children equally, they worry most about the sick child.' T’ien-t’ai, commenting on this sutra passage in his Great Concentration and Insight, said, 'Even if the parents of seven children are never partial, they are still particularly concerned about the sick one.' In essence, the sutra is saying that, even if there are many children, the parents’ hearts are with the child who is ill. To the Buddha, all living beings are his children. Among them, the sinful man who slays his own parents and becomes an enemy of the Buddha and the sutras is like the sick child." (Winter Always Turns to Spring).