In these two passages Hume is making two distinct but related points. First, he maintains that “action”, considered as an “external performance” without any reference to the motive or intention that produced it, is not itself of moral concern. It is, rather, the “internal” cause of the action that arouses our moral sentiments. It is these aspects of action that inform us about the mind and moral character of the agent. Second, the moral qualities of an agent that arouse our moral sentiments must be “durable or constant” – they cannot be “temporary and perishing” in nature in the way actions are. This second condition on the generation of moral sentiment is itself a particular instance of the more general observation that Hume has made earlier on in Book II that the relationship between the quality or feature that gives rise to the indirect passions (i.e., its cause) and the person who is the object of the passion must not be “casual or inconstant” (T 2.1.6.7/293). It is, nevertheless, the first point that is especially important for our present purpose of understanding why necessity is essential to morality.