This is done in order to transfer the genetic information to the new cells formed. Hence the daughter cells formed have the same genetic makeup as their parent cells.
When the cell divides even the blueprint i.e. DNA should be given to it for building up of the organism. The cell divides into two and distributes each copy of DNA into the divided cells. Through replication the DNA transfers the information necessary for creating an exact copy of it in the new cell. The copy is created in order to continue the species. Through DNA replication the organism is able to reproduce the genetic code and transfer it to the next generation.