American clergyman and activist Martin Luther King, Jr. (1929-1968) wrote in the book Strength to Love (1963):
   
“Light has come into the world, and every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, ‘What are you doing for others?’”
 
The quote is similar in theme to what King said in “Conquering Self-centeredness,” a sermon delivered at Dexter Avenue Baptist Church in Montgomery, Alabama, on August 11, 1957, but “What are you doing for others?” was not said there.
 
King’s birthday became a national holiday and then a national day of service in the 1990s. King’s quotation of “What are you doing for others?” is often used as a theme for the day of service.
 
“What are you doing for others?” had been cited in Christian literature since at least 1907.
 
   
Wikipedia: Martin Luther King, Jr.
Martin Luther King, Jr. (January 15, 1929 – April 4, 1968) was an American clergyman, activist, and leader in the African-American Civil Rights Movement. He is best known for his role in the advancement of civil rights using nonviolent civil disobedience. King has become a national icon in the history of American progressivism.
 
Wikiquote: Martin Luther King, Jr.
Conquering Self-centeredness (1957)
Sermon Delivered at Dexter Avenue Baptist Church in Montgomery, Alabama (11 August 1957)
An individual has not begun to live until he can rise above the narrow horizons of his particular individualistic concerns to the broader concerns of all humanity. And this is one of the big problems of life, that so many people never quite get to the point of rising above self. And so they end up the tragic victims of self-centeredness. They end up the victims of distorted and disrupted personality.
. Variants (Many of MLKs’ speeches were delivered many times with slight variants): An Individual has not started living fully until they can rise above the narrow confines of individualistic concerns to the broader concerns of humanity. Every person must decide at some point, whether they will walk in light of creative altruism or in the darkness of destructive selfishness. This is the judgment: Life’s most persistent and urgent question is: ‘What are you doing for others?’
As quoted in The Words of Martin Luther King, Jr. by Coretta Scott King, Second Edition (2011), Ch. “Community of Man”, p. 3
 
Wikipedia: Martin Luther King, Jr. Day
King Day of Service
The national Martin Luther King Day of Service was started by former Pennsylvania U.S. Senator Harris Wofford and Atlanta Congressman John Lewis, who co-authored the King Holiday and Service Act. The federal legislation challenges Americans to transform the King Holiday into a day of citizen action volunteer service in honor of Dr. King. The federal legislation was signed into law by President Bill Clinton on August 23, 1994. Since 1996, the annual Greater Philadelphia King Day of Service has been the largest event in the nation honoring Dr. King.
 
Several other universities and organizations around the U.S., such as Arizona State University, Greater DC Cares and City Year, participate in the Dr. Martin Luther King, Jr. Day of Service. In honor of MLK, volunteers across the country donate their time to make a difference on this day.
   
Google Books
The Call of the Father
By Right Rev. Arthur Foley Winnington Ingram, Lord Bishop of London
London: Wells Gardner, Darton & Co.
1907
Pg. 12:
Are you a Churchman? What are you doing for others?
 
Google Books
Kingdom Songs:
For use in the Sunday School, the Young People’s Meeting, the Devotional Service
Edited by C. Harold Lowden, Rufus Wilder Miller
Philadelphia, PA: Heidelberg Press
1914
Pg. 98:
What are You Doing for Others?
Mrs. C. D. Martin. W. Stillman Martin
 
18 June 1922, Palatka (FL) Daily News, pg. 4, col. 6 ad:
What Are You Doing For Others?
(...)
THE FIRST BAPTIST CHURCH
 
Google Books
Strength to Love
By Martin Luther King, Jr.
New York, NY: Harper & Row
1963
Pg. 88:
Light has come into the world, and every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, “What are you doing for others?”
 
Google Books
I Have a dream:
The Quotations of Martin Luther King, Jr.
By Martin Luther King, Jr.
New York, NY: Grosset
1968
Pg. 2:
ALTRUISM
Every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, “What are you doing for others?”
   
31 October 1968, Ottawa (ON) Journal, pg. 6, col. 2:
‘What Are You Doing For Others?’
The Christmas Card of the Primate of the Anglican Church, and Mrs. Howard Clark, presented a message of poignant significance not only for Christmas but on the eve of the New Year. It offered these words of Martin Luther King, Jr.:
 
“Light has come into the world, and every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, what are you doing for others?”
 
Google Books
The Words of Martin Luther King, Jr.: Second Edition
By Martin Luther King
Selected by Coretta Scott King
New York, NY: Newmarket Press
1983
Pg. 17:
“An individual has not started living until he can rise above the narrow confines of his individualistic concerns to the broader concerns of all humanity.”
 
“Every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, What are you doing for others?”
 
“Everybody can be great, because everybody can serve. You don’t have to have a college degree to serve. You don’t have to make your subject and your verb agree to serve. You don’t have to know about Plato and Aristotle to serve. You don’t have to know Einstein’s theory of relativity to serve. You don’t have to know the second theory of thermodynamics to serve. You only need a heart full of grace. A soul generated by love.”
 
Google Books
Black Womanist Ethics
By Katie G. Cannon
Atlanta, GA: Scholars Press
1988
Pg. 22:
King argues that life’s most persistent and urgent question is “What are you doing for others?” Repeatedly in his writings and sermons, King emphasizes the Christian’s social responsibility to work toward social change which would usher in the beloved community.
 
Google Books
Africa: We Owe It to Our Ancestors, Our Children, And Ourselves
By Michael Ba Banutu-Gomez
Lanham, MD: Hamilton Books
2006
Pg. 124:
How responsible am I for the well-being of my fellows? To ignore evil is to become an accomplice to it. An individual has not started living until he can rise above the narrow confines of his individualistic concerns to the broader concerns of all humanity. Every man must decide whether he will walk in the light of creative altruism or the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, “What are you doing for others?” Everybody can be great, because everybody can serve. You don’t have to have a college degree to serve. You don’t have to make your subject and your verb agree to serve. You don’t have to know about Plato and Aristotle to serve. You don’t have to know Einstein’s theory of relativity to serve. You don’t have to know the second theory of thermodynamics to serve. You only need a heart full of grace. A soul generated by love.
 
The White House Blog
MLK Day: What Are You Doing for Others?
Patrick A. Corvington
January 14, 2011 06:07 PM EST
This Monday, Americans across the nation will honor Dr. King and mark the 25th anniversary of the holiday that bears his name.  Sixteen years ago, Congress passed legislation transforming the King holiday into a national day of service.  We’ve seen it grow from a handful of local events to well over 13,000 projects taking place this year in all 50 states.
(...)
To mark the 25th anniversary of the holiday, and to continue the momentum for the MLK Day of Service throughout the year, on Monday we are launching the MLK 25 Challenge: What Are You Doing for Others? This initiative calls on Americans to honor Dr. King by pledging to take at least 25 actions during 2011 to make a difference for others and strengthen our communities.
 
Tampa Bay Online
Answering Martin Luther King’s question, ‘What are you doing for others?’
By TBO.COM | Staff
Published: January 21, 2013
The Corporation for National and Community Service recently released a new report about volunteerism in America, with highlights including the fact that parents are volunteering significantly more than their childless counterparts.
(...)
Martin Luther King so famously said, “Life’s most persistent and urgent question is: What are you doing for others?” Together, let’s create a culture where our children have the opportunity to begin answering that question now. I can’t think of a more effective or efficient way to improve our kids and our communities, for today and for tomorrow, than by calling on our kids to serve.
   
Greeneville (TN) Sun
Originally published: 2013-01-22 10:39:58 Last modified: 2013-01-22 10:41:05
Volunteers Observe King Holiday
By Helping At Soup Kitchen
BY SARAH GREGORY
STAFF WRITER
“An individual has not begun to live until he can rise above the narrow horizons of his particular individualistic concerns to the broader concerns of all humanity.
 
“Every person must decide, at some point, whether they will walk in the light of creative altruism or in the darkness of destructive selfishness. This is the judgment. Life’s most persistent and urgent question is, ‘What are you doing for others?’”—Dr. Martin Luther King Jr., in a sermon, Sunday, Aug. 11, 1957.