Answer:
so that mistakes from the past won't be done again.
it would be foolish to believe in something that failed over and over again, or led to great suffering.
by knowing the past we can influence the future in better ways. over great length of time we can draw conclusions wich effects certain decisions and policies have, wich we can't do ad hoc in the present.
in a broader context, world history offers even more insights how things were done in the past.
it's of course also useful to look what worked well before and why we do things we do today.
the word "true" might also refer to getting rid of cultural, political or family based biases and empty presumptions that are in hindsight hard to defend.
this text/answer isn't meant to be directly political, or to favor any one side.
