“If we must die, O let us nobly die,
So that our precious blood may not be shed
In vain; then even the monsters we defy
Shall be constrained to honor us though dead!”

Pelopidas, sec. 1
Parallel Lives

SF was an abbreviation for "Supreme Fascist" — the term Erdős often used to refer to God, as quoted in The Man Who Loved Only Numbers : The Story of Paul Erdős and the Search for Mathematical Truth (1998) by Paul Hoffman, p. 4

Variant: Let us endeavor so to live that when we come to die even the undertaker will be sorry.
Source: Pudd'nhead Wilson

1960s, A Time for Choosing (1964)
Context: The martyrs of history were not fools, and our honored dead who gave their lives to stop the advance of the Nazis didn't die in vain. Where, then, is the road to peace? Well, it's a simple answer after all. You and I have the courage to say to our enemies, "There is a price we will not pay." There is a point beyond which they must not advance. This is the meaning in the phrase of Barry Goldwater's "peace through strength." Winston Churchill said that "the destiny of man is not measured by material computation. When great forces are on the move in the world, we learn we are spirits — not animals." And he said, "There is something going on in time and space, and beyond time and space, which, whether we like it or not, spells duty."

First Journal of Travel (1840)

Letter to Sisters at Saint Mary's, 1848.
Context: Let us never forget that if we wish to die like the Saints we must live like them. Let us force ourselves to imitate their virtues, in particular humility and charity.

Source: Dr. Faustus

During negotiations with Crook and others, in [Books on Google Play Congressional Serial Set, 1890, U.S. Government Printing Office, https://books.google.com/books?id=lQ0ZAAAAYAAJ, 1 March 2018, 59]

Source: The Sea