What does Marcus Aurelius say is truly indifferent versus in our power?

Marcus draws the line inside himself, not between himself and the world. In Meditations 6.32 he writes: "I consist of a little body and a soul." The body, he says, cannot even perceive differences, so all things are indifferent to it. But to the understanding, "those things only are indifferent, which are not the works of its own activity." Whatever the mind itself does is in its power. And even here he narrows the claim further: only what the mind does now, in the present, is truly in its power. Past and future activities of the mind are, for the present moment, also indifferent (Meditations 6.32).

This is a stricter claim than most people expect. The common reading of Stoic indifference treats it as a rough sorting of life into two piles: externals like health, money and reputation on one side, and your choices on the other. That is not wrong, but Marcus pushes past it. He is not just saying external things do not matter as much as your character. He is saying that even your own mind's past judgments and future intentions, once they are not the present act of judging, fall into the same category as the little body's sensations. They are not currently the work of your faculty of choice, so they are not currently yours to claim as good or bad. Only the live act of understanding, happening right now, is in your power.

Elsewhere Marcus gives the reason this matters. In a passage on the same theme he lists death, life, honor, dishonor, pain and pleasure, and observes that these "equally happen to good men and bad, being things which make us neither better nor worse" (Meditations 2.11). If something falls on the good and the wicked without distinction, it cannot be the thing that makes a life good or bad, because then providence would have let good and evil land at random. Since Marcus holds that the nature of the universe does not overlook this or lack the skill to prevent it, he concludes that these things are neither good nor evil. That is the ethical stakes: indifference is not indifference to consequences, it is a claim about what can and cannot make you a better or worse person.

Notice what changes if you take this seriously. You stop asking whether an outcome, an injury, a promotion, a diagnosis, was good or bad for you, because none of these can touch your character. You start asking only whether your present judgment about it is sound. The question moves from what happened to me to what am I doing with my mind right now. That is a demanding shift because it means you cannot rest on your past good judgments either. Yesterday's wisdom is, on this passage, already indifferent. Only the work your understanding is doing this moment counts.

The concrete practice this suggests is simple to state and hard to sustain: when something happens, whether it is a small annoyance or a serious loss, ask what your mind is doing with it right now, not what it did with something like it before and not what you plan to do about it later. Bring the question back to the present act of judgment, because that is the only place, according to Marcus, where anything is actually in your power.