But I think the American people expect more from us than cries of indignation and attack. The times are too grave, the challenge too urgent, and the stakes too high — to permit the customary passions of political debate. We are not here to curse the darkness, but to light the candle that can guide us through that darkness to a safe and sane future.

John F. Kennedy (1917–1963) American politician, author, journalist, US President (1961–63)

Speech (1960-07-15), “The New Frontier,” Presidential Nomination Acceptance Speech, Democratic National Convention, Memorial Coliseum, Los Angeles
    (Source)

(Source (Video))

Though this remains the official text of the speech, Kennedy left most of this passage out in delivering it, leaving only: "We are not here to curse the darkness; we are here to light a candle."

The darkness/candle phrase, in turn, originated in a 1907 sermon by W. L. Watkinson.