It is a refrain among many young people today and an unquestioned good that they want to change the world. This statistically significant surge in things like volunteering, donating and civic engagement has been celebrated as a virtue of millennials and our successors, Generation Z, compensating for our digital addictions and other shortcomings. It has been encouraged by teachers and other elders, perhaps especially by those at a loss about how to change the world themselves.

After a few decades of inhabiting this doctrine wholeheartedly, those words—“change the world”—have come to feel exhausting. Maybe this is the inevitable aging of an early millennial, slightly ahead of a curve, that will soon be a generational about-face; maybe it is the sigh of a faint heart. But no: Now, to me, it is talk of changing the world that sounds faint.

For one thing, the phrase always seems to come at the end of a sentence—change the world, period. Change the world how? Fortunately, young people in America have grown freer from the alleged permanence of capitalism, but the revolutions on offer tend to fall short of, say, those of Karl “the point is to change it” Marx. When explained further, the world-changing I hear about typically involves a targeted intervention on the order of what a tech startup or a particularly effective N.G.O. might achieve.

The phrase always seems to come at the end of a sentence—change the world, period. Change the world how?

The implication seems to be that any change is better than none. The world is that bad, I guess.

As with all lazy talk about generations, there is a missing story here of class divides, where the supposed universal is actually a particular. Some kids are told they can and should change things, while others are told to keep their heads down no matter what. Heard that way, the rote dream of world-changing bears echoes of old tropes of the “white man’s burden,” idolatrous saviorism and the so-called philanthropy that Anand Giridharadas has rightly called “the elite charade of changing the world.”

Saviorism should seem especially repulsive among Christians, followers of a Messiah who defied expectations that he would upend the political order in specific ways. Instead, he was killed. It took a few hundred years for people claiming his mantle to witness the fall of the Roman Empire, right when they thought they had conquered it for themselves.

Greta Thunberg has recently landed by sailboat on our shores, Jonah-like, to speak sense to our calamitous leaders.

What the world might need most is for people to do less. I have several international flights ahead of me before the year’s end, all in the service of dubious world-changing; isn’t it probable that my greater contribution to planetary survival would be to cancel them? My students tell me about the crushing burden of expectation they feel when social media feeds bombard them with the amazing doings of their contacts; might we all be healthier if we accomplished and broadcasted less?

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I do not want to give up on vigor entirely, however. That part of our humanity, along with leisure, is a gift. Courage, perseverance and vision are fearsome things, as you know if you have ever beheld them up close.

Those characteristics bring me to Greta Thunberg, the 16-year-old Swede who has recently landed by sailboat on our shores, Jonah-like, to speak sense to our calamitous leaders.

To be a healer means your motivation begins like this: What do you love, what do you protect, what do you refuse to harm?

She might seem like a poster child for world-changing of the kind I have been talking about. But she and her popularity (including with my own children) suggest my accusations against the young may be unfounded. Ms. Thunberg rejects saviorism at every turn, insisting that she would much rather be back at home in school and be done with this climate crusade. She also appears less concerned with changing the world than with articulating a rather conservative desire to protect it—to protect species from dying out, to protect a habitable world for future human beings, to protect the dignity of scientific reason from further assaults by greed. Yes, addressing climate change requires radical upheavals in how we live and what we prioritize, but that is not her fault. She would prefer that being good stewards of the Earth were easier.

Rather than saviorism, I think of Ms. Thunberg’s ethic as following the Jewish notion of tikkun olam, or healing the world. To heal means focusing first of all on protecting what one loves, what we know to be good. If doing so requires drastic change, as Thomas Aquinas would put it, that is that.

To be a healer means your motivation begins like this: What do you love, what do you protect, what do you refuse to harm? What is worth more than the illusions we cling to? “We are at the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth?” Ms. Thunberg demanded at the United Nations on Monday. She allowed that world leaders might be “evil”—if they knew the consequences of their inaction and still did nothing—but chose to believe that they are not.

Healing begins not with disruption or innovation but with listening, with a humility that knows the body is its own best healer. Healing is enabling and rousing, not imposing. Perhaps Ms. Thunberg testifies that when other young people talk about changing the world, what they mean is actually more along the lines of healing what they inherit.

Nathan Schneider is a professor of media studies at the University of Colorado Boulder. He is the author of Governable Spaces: Democratic Design for Online Life and God in Proof: The Story of a Search From the Ancients to the Internet.