In the Light of Truth: The Grail Message was written by Oskar Ernst Bernhardt (1875–1941), and first published in 1926 under the pen name Abd-ru-shin. An expanded, complete edition was published by the author under the name of Abdruschin in 1931, entitled Im Lichte der Wahrheit (In the Light of the Truth). It was a collection of 91 lectures, written to build upon each other, presenting a complete picture of Creation. Between 1931 and 1934, a further total of 59 additional lectures were released.

Abd-ru-shin went on to write and publish more than 50 individual lectures after 1934, however the deteriorating conditions in Europe prevented him from publishing any further books during his lifetime. When the Nazis seized power in Austria in 1938, Abd-ru-shin was arrested, extradited to Germany, and kept under house arrest until his death in December 1941.

During his final years, Abd-ru-shin was forbidden by the Gestapo from working on the Grail Message. Abd-ru-shin never authorized any changes after publishing his 1931 version. In fact he wrote "I do not hand over the Message so that you can deal with It as you see fit in your efforts to transmit It to humanity, but I COMMAND that It must remain immutable in all that It contains and in the way It is! Whoever will change even the slightest meaning, the smallest word, even with the best intention, is guilty of wrongdoing! It is the Holy Word of God, which man may not touch in order to adapt It in a way more convenient for himself or for easier understanding by indolent human spirits!"

Abd-ru-shin is a self-proclaimed Messiah according to the original 1931 edition of The Grail Message, in particular the Conclusion of the 1931 edition. He removed the explicit statement of that claim from the 1937 and later editions. But it still is the meaning for the Message of the Grail that Abd-ru-shin is the apocalyptic Son of Man.