Dr. Martyn Lloyd-Jones preached this sermon titled “By This Shall All Men Know…” at the Evangelical Alliance Ministers’ Conference in 1969, stressing the importance of supplementing the reading of theology with that of history. He encouraged avoiding being abstractly academic without applying theological truths to daily life and to look at the “generals” in history to keep the “particulars” of theology realistic. Listen to what the Roman Catholics said about Protestantism. Who do the facts support? Learn about the denominational divisions of Christianity. If many are based merely on comprehension, are they justified or sinful? Learn of the factors that caused such divisions. Hear of the national churches that hindered the Protestant union and how spiritual elements were overwritten by political ones. Hear of the history of Calvin, Luther, Anabaptists, Presbyterians, and many others. Dr. Lloyd-Jones discusses episcopacy and tradition, essentials and non-essentials, and striving for Protestant union. He shares the significance of the Westminster Confession and other confessions of faith. Avoid the extremes of unrestrained laxity and egotistical rigor, define the differences between error and heresy, and heed the call to be charitable.