This is really two quotations in one. The more famous element ends after 'equal'. Most non-Americans would be hard-pressed to continue the quotation and get as far as 'happiness'. But the plural form 'truths' shows that there is more to be said than just the point about equality, and this motivates the longer version. There are few quotations which exceed this one for general applicability; and few where it has proved so necessary to keep asserting the insight it expresses.