Christian witness: speaking truth to power

Dorothy Day (1897-1980) on Wikipedia and as a woman of conscience, the founder of the Catholic Worker Movement, and perhaps even a saint

Thomas Merton (1915-1968) on Wikipedia and Goodreads, in audio clips, and in articles in Aeon and the New Yorker

William Stringfellow (1928-1985) on Wikipedia and Goodreads, in Sojourners

Rev. Martin Luther King, Jr. (1929-1968) in speeches and sermons and on Goodreads
(The first video, “The Other America,” opens with a lot of static)

Desmond Tutu (b. 1931) on Wikipedia and Goodreads, and in his Nobel Peace Prize speech.

Joan Chittester (b. 1936) on her own website, with its podcasts, on Wikipedia, in conversation with Maria Shriver, and in her TEDxWOMEN talk

Some contemporary Christian writers

Madeleine L’Engle (1918–2007)
On Wikipedia and Goodreads
In the New Yorker (2004)
Interviewed by young readers of Scholastic

David Steindl-Rast (b. 1926)
On Wikipedia and Goodreads
Death & Spirituality (Kenneth Kramer interviews on video)
Want to Be Happy? Be Grateful (TED Talk, 2013)
Words of Common Sense for Mind, Body, and Soul

Henri Nouwen (1932-1996)
On Wikipedia and Goodreads
An interview from The Ligourian (1992)
Being The Beloved“: sermon series at the Crystal Cathedral (1992)

Wendell Berry (b. 1934)
On Wikipedia and Goodreads
His interview with Bill Moyers (2013)
His interview in the New Yorker (2019)

Kathleen Norris (b. 1947)
On Wikipedia and Goodreads
Her interview with BeliefNet (2008)
On the “Encountering Silence” podcast: Part I and Part II (2018)

Garret Keizer (b. 1953)
On Wikipedia and Goodreads
On Organized Religion
The Enigma of Anger

Ann Lamott (b. 1954)
On Wikipedia and Goodreads
Her Facebook page
Her TED Talk: “Everything I Know For Sure” (2017)
Her interview with LitHub (2018)

Rachel Held Evans (1981-2019)
On Wikipedia and Goodreads
On the “Darkwood Brew” podcast (2011)
Interview with Pete Enns (2019)

Some classic Christian writers

Many more may be found in the Christian Classics Ethereal Library and at Project Gutenberg, which both offer free downloads. Here is a sampling through the ages:

St. Augustine (354-430):
The Confessions
The City of God: Part I and Part II

Hildegard of Bingen (1098-1179):
Select Writings

Meister Eckhart (1260?–1328?)

Ugolino of Montegiorgio (1262?-1348?):
The Little Flowers of Saint Francis

Julian of Norwich (1342-1416):
Revelations of Divine Love

Margery Kempe (1373?–1440)
The Book of Margery Kempe

Teresa of Avila (1515–1582)
The Life of Teresa of Jesus
Interior Castle, or The Mansions

St. John of the Cross (1542-1591)
Ascent of Mt. Carmel
Dark Night of the Soul

Brother Lawrence of the Resurrection (c. 1614–1691)
Practice of the Presence of God

Blaise Pascal (1623-1662):
Pensees (sample quotes here)

John Wesley (1703-1791)
A Short History of Methodism

John Woolman (1720–1772)
The Journal of John Woolman

John Henry Newman (1801–1890)
Apologia pro Vita Sua

Frederick William Robertson (1816–1853)
Sermons Preached at Brighton
Life and Letters of F.W. Robertson
Marilyn Thomas on Robertson
Marilyn Thomas on his secret diary

Vladimir Solovyov (1853–1900)
Divine Sophia (Kornblatt, ed. 2009)
The Meaning of Love (1894) quotes on Goodreads
A sampler edited by Paul Valliere
War, progress, and the end of history, including a short story of the Anti-Christ (1915)
Solovyov quotes on Goodreads

G.K. Chesterton (1874-1936):
Heretics (read aloud here)
Orthodoxy (sample quotes here and here, read aloud here)
The Everlasting Man (sample quotes here, read aloud here)
The Wisdom of Father Brown
Chesterton quotes on Goodreads

Dorothy L. Sayers (1893–1957)
Creed or Chaos (quotes on Goodreads, chapter 6 here)
Strong Meat” and “The Greatest Drama Ever Staged
The Man Born to Be King
The Mind of the Maker

Thomas R. Kelly (1893–1941)
Holy Obedience (1939)
Testament of Devotion
The Eternal Promise (“The Gathered Meeting” and “Hasten Unto God”)
Quotes on Goodreads

C.S. Lewis (1898-1963)
A Grief Observed (read aloud here)
Mere Christianity (read by Geoffrey Howard here)
Surprised by Joy (read aloud here)
Audio clips, quotes from Goodreads

Elton Trueblood (1900–1994)
The Humor of Christ (1964)
An Introduction to Quakers (1964)
A Place to Stand (1968)
The Predicament of Modern Man (1944)
Quotes on Goodreads

Douglas Steere (1901–1995)
Doors into life : through five devotional classics (1981) excerpt only
The Open Life (1937)
Prayer and Worship (1938) excerpt only
A Steere quote on Goodreads

Dag Hammarskjöld (1905-1961)
Markings (1963)
Quotes on Goodreads

Christian poets

Poems by Francis of Assisi (1182-1226)
Poems by Dante Alighieri (1265-1321)
Poems by Robert Southwell (1561-1595)
Poems by John Donne (1572-1631)
Poems by George Herbert (1593-1633)
Poems by John Milton (1608-1674)
Poems by Anne Bradstreet (1612-1672)
Poems by Isaac Watts (1674-1748)**
Poems by Charles Wesley (1707-1788)**
Poems by William Blake (1757-1827)
Poems by Emily Dickinson (1830-1886)
Poems by Christina Rosetti (1830-1894)**
Poems by Gerard Manley Hopkins (1844-1889)
Poems by T. S. Eliot (1888-1965)
Poems by W.H. Auden (1907-1973)
Poems by Richard Wilbur (1921-2017)
Poems by Vassar Miller (1924-1998)
Poems by Luci Shaw (b. 1928)
Poems by Wendell Berry (b. 1934)
Poems by Jean Murray Walker (b. 1944)

** You can also just look in your hymnals!

Christian allegory

John Bunyan (1628-1688):
Pilgrim’s Progress

George MacDonald (1824-1905):
The Princess and the Goblin, read by Andy Minter here
The Princess and Curdie, read by Lizzie Driver here
The Light Princess/The Giant’s Heart/The Golden Key

C.S. Lewis (1898-1963):
The Chronicles of Narnia
The Screwtape Letters, read aloud here
The Great Divorce, read aloud here

Madeleine L’Engle (1918-2007)
A Wrinkle in Time, read aloud
A Wind in the Door
A Swiftly Tilting Planet, read aloud 
Many Waters, read aloud
An Acceptable Time, read aloud

A Sampling of Anti-Christian Writers

Samuel Butler (1835–1902)
On churches (from Erewhon) and messianic religion (from Erewhon Revisited)

Mark Twain (1835–1910)
On religion and Christianity

Bertrand Russell (1872–1970)
Why I Am Not a Christian” (1927, read aloud by Terrence Hardiman here)

Richard Dawkins (b. 1941)
The God Delusion on Goodreads and the CBC’s The Hour, Outgrowing God on BBC4

Christopher Eric Hitchens (1949–2011)
God is Not Good on Goodreads and Wikiquote, and an excerpt in Newsweek