Kipling himself took inspiration from the Bible - namely Deuteronomy 6 verse 12, which reads: "Then beware lest thou forget the Lord which brought thee forth out of the land of Egypt". The poem doesn't touch upon remembering fallen soldiers, but has been adopted as part of Armistice Day traditions.

Is it lest we forget or lest?

"Lest we forget" is a phrase commonly used in war remembrance services and commemorative occasions in English speaking countries. ... The phrase occurs eight times; and is repeated at the end of the first four stanzas in order to add particular emphasis regarding the dangers of failing to remember.

Why do we say lest in Lest we forget?

Lest we forget—lest we forget! 'Lest' is Old English for 'less that', and the word gained popularity around the time the poem was written. It became part of a phrase to honour the past sacrifices of those who had served and lost their lives and to never forget.