Why not "Freedom is important for all"?
According to what I learned, the preposition 'for' changes the meaning to "It is important that all people are free", which is rather not the meaning of the Polish sentence.
Star341179. I agree. The gramatical explanation has no weight on the widely used used explanation as in this case "for all" means everyone.
Why not freedom is important for everyone why is dla read here as to and not for?
OK, we'll change the main answer to "for everyone".
All pretty much means everyone.
Freedom is essential for everyone
Essential means crucial or indispensable. The word 'important' alone doesn't have this connotation.
In Polish you'd probably say "jest niezbędna".