James Stone wrote:
The phrase "Lest we forget" is commonly used in war remembrance services and commemorative occasions in English speaking countries, in particular Remembrance Day and ANZAC Day.[1] Before the term was used in reference to soldiers and war, it was first used in an 1897 Christian poem written by Rudyard Kipling called "Recessional". The phrase occurs 8 times; and is repeated at the end of the first 4 stanzas in order to add particular emphasis regarding the dangers of failing to remember.
WIKIPEDIA D: