What does Roosevelt mean when he says the United States will "make it very certain that this form of treachery shall never again endanger us"?

President Franklin D. Roosevelt addressed a speech to the U. S Congress in which he mentions "make it very certain that this form of treachery shall never again endanger us."

His speech took place on December 7 in 1941 after Japan attacked the U. S.

With these words, president Roosevelt asked the Congress to declare war on Japan. His main objective was to convince the members of the Congress of the grave danger that Japan represented for the country, thus, they had the responsibility to counterattack.