According to a 16th-century rumor, as doomsday preachers prophesied the end of times, Martin Luther replied to a question about how to live in the face of apocalyptic collapse—to live in a society on fire with plagues and famines, with political revolt and religious upheaval. “If I knew the world would end tomorrow,” Luther responded, “I would plant a tree this afternoon.”

Last year I planted a tree in our backyard. A black gum, Nyssa sylvatica. The species is native to the eastern regions of North America. Up the coast in New York, arborists have documented clusters of them that are more than 500 years old. My black gum will grow into maturity long after my body returns to the dust.

At least that’s my hope: for the tree to experience several centuries of life. It’s a modest hope, but it seems increasingly audacious with every new climate report and every trivial response from our elected leaders, their cruel negligence of earthly life. I plant and water even though our future feels like guesswork. We add saplings for the sake of the beauty of the earth, even if that beauty is fleeting. We flood the streets with protest, even as politicians double down on their shilling for the fossil fuel industry. An ethical life, as we confront an environmental apocalypse, is a prayer we offer with our bodies—marching as supplication, planting as invocation. My sapling is a hope against hope, as the apostle Paul wrote, to believe in the God who calls into existence possibilities that do not exist: impossible futures.

During the last years of the Second Temple period, as the people of Jerusalem longed for a messianic interruption of Rome’s violent occupation, the esteemed rabbi Yohanan ben Zakkai spoke about trees. “If you have a sapling in your hand and they tell you that the Messiah has arrived,” he said, “first plant the sapling and then go out to greet him.” In a world of revolutionary fervor and apocalyptic hope, Zakkai turned his people’s attention to a tree and the soil.

Overlooking my sapling in the backyard, the arms of an old willow oak stretch a canopy of leaves across the sky. The tree is at least 150 years old, an arborist told me a while ago. I wish I knew how to ask the oak what it has witnessed over those years—to ask, for example, what those days, weeks, and months after the Emancipation Proclamation sounded like as Black residents freed themselves from White enslavers, a time when liberation wafted into the heavens, the neighborhood trees alive with the breath of hope.

I first thought about trees as witnesses to our lives when I noticed the single oak in the background of Andrei Rublev’s 15th-century icon The Trinity. The image depicts Abraham and Sarah offering hospitality to the three visitors who turn out to be God “by the oaks of Mamre” (Gen. 18:1). At the top edge of the frame, an oak bends over the three divine visitors who sit around a table below. The bushy tree leans toward them as if listening, as if watching, as if drawn into the perichoresis, a communion of breath drifting through the air. The ancient oak bears witness to Sarah and Abraham’s theophany.

In 2016 I visited the holy site where pilgrims have long journeyed to venerate Mamre’s oaks. A mile west of the old city of Hebron/Al-Khalil, on the outskirts of an industrial zone, the weathered remnants of a rugged tree—buttressed with metal braces—stand outside the doors to the Church of the Holy Forefathers on the grounds of the Russian Orthodox Monastery of the Holy Trinity. A monk welcomed me to the compound and escorted me up the hill to the vestige of the scene in Genesis. I walked slowly around the tree, then around again, lost in wonder. What does it mean for this holy landscape, this dead witness, to bear the traces of that visitation long ago?

The monk opened the creaky church door and invited me to wander through the sanctuary. As he lit candles, the icons on the walls flickered to life. My eyes followed the shimmer from one depiction of the scene at Mamre to another—icons of icons, each resplendent in a sacred aura, the Trinity and the tree.

Outside, as we walked back down the hill, I asked the young monk how long he’ll live here. “The rest of my life,” he said, “if there is no war.” As he blessed me with a farewell, I glimpsed the silhouette of the dead oak on the hill behind him, and I remembered an old story, a medieval rumor: that when the last oak of Mamre withers and dies, then the end of the world will begin.

Since my visit, the monks have noticed a slender stem poking from the decayed wood—one green sprout, then another. The ancient roots, dormant for some time but now enlivened, have awakened hungry for the sun. The tree has not given up being a witness. It has not given up on us, even if our human civilization seems to have given up on the health of the planet. The oak at Mamre—like the oak in my backyard, like saplings everywhere—remains, bearing witness and reminding us of God’s visitations.