Why is it necessary for dna to replicate as the first step in mitosis?

It's necessary for DNA to replicate as the first step in mitosis because the whole point of mitosis is to create new cells, exactly like the old ones. Since DNA has all the genetic information that makes cells do what they do, it's necessary to replicate them in the act of mitosis.

Alright, i'm gonna try to explain this as good as possible. the law of conservation is like a collection overtime. it never changes though. no matter how you change the constituent parts.