In 1911 Chambers founded and was principal of the Bible Training College in Clapham Common, Greater London, in an "embarrassingly elegant" property that had been purchased by the Pentecostal League of Prayer.
Chambers accommodated not only students of every age, education, and class but also anyone in need, believing he ought to "give to everyone who asks." "No one was ever turned away from the door and whatever the person asked for, whether money, a winter overcoat, or a meal, was given."
Between 1911 and 1915, 106 resident students attended the Bible Training College, and by July 1915, forty were serving as missionaries.
In 1915, a year after the outbreak of World War I, Chambers suspended the operation of the school and was accepted as a YMCA chaplain. He was assigned to Zeitoun, Cairo, Egypt, where he ministered to Australian and New Zealand troops, who later participated in the Battle of Gallipoli.
Chambers was stricken with appendicitis on 17 October 1917 but resisted going to a hospital on the grounds that the beds would be needed by men wounded in the long-expected Third Battle of Gaza.
On 29 October, a surgeon performed an emergency appendectomy, but Chambers died 15 November 1917 from a pulmonary hemorrhage. He was buried in Cairo with full military honors.
Before he died, Chambers had proofread the manuscript of his first book, Baffled to Fight Better, a title he had taken from a favorite line by Robert Browning.
For the remainder of her life—and at first under very straitened circumstances—Chambers' widow transcribed and published books and articles edited from the notes she had taken in shorthand during the Bible College years and at Zeitoun.
Most successful of the thirty books was My Utmost for His Highest (1924), a daily devotional composed of 365 selections of Chamber's talks, each of about 500 words. The work has never been out of print and has been translated into 39 languages.