When did Martin Luther King say this The ultimate measure of a man is not where he stands in moments of comfort and convenience, but where he stands in times of challenge and controversy”
This quotation is from Martin Luther King's book, Strength to Love, a collection of his sermons, edited by Melvin Arnold and Charles Wallis and published in 1963 by Harper and Brother's Religious Books.
There are plenty of explanations of the meaning of this quotation, including the eNotes reference below, but it is important to assess its message: namely, that men and women who have the courage and strength to live out their moral beliefs, even in the face of adversity, are the true champions in this world.
King's Strength to Love contained very many messages for the America and global public, some of which appeared too strong for its readers, or perhaps the political leadership, and which were subsequently removed by editors Arnold and Wallis. See the Stanford University King Institute Encyclopedia for further information.