Why is it important for DNA to make an accurate copy of itself?

If DNA messes up and doesn't make accurate copies, there might be a LOT of unwanted mutations and the organisms that result out of that copy might end up dead or with some serious deformities. Most (if not all, probably all) genetic diseases and mutations are results of mistakes in the proces.

When the DNA is being copied inside the nucleus of the cell, there are a lot of enzymes that help speed up the process and replace wrong nucleobases. There is topoisomerase, helicase, polymerases and gyrase.

You'll have to search for the exact function of them yourself, because my English isn't good enough to explain that..