why must the nuclear membrane dissolve during prophase?

Answer 1

This is required to ensure the free movement of the chromosomes to the equatorial plate and to two opposite poles.

Answer 2

This is needed so the chromosomes, which are located in the nucleus, can align along the metaphase plate. It is during this stage that the chromosomes are pulled apart. Thus, when the cell divides in two, each daughter cell has a set of chromosomes. That is the fast and easy answer. It is much more complicated than this.

Answer 3

because the chromonsones have to be eventually sorted into two seperate nuclei.